TLDR; Just speculating about the potential for more classic cartoons returning to US broadcast television on various OTA diginets. I'm not an expert, not connected, have no real industry insight, and don't know anybody or anything. I have assumptions and things I think I know, but am likely wrong on some points.
With what has happened now with the first initial broadcasts of classic theatrical cartoons on MeTV, which is significant in several ways, I thought I'd explore where things could go from here if there were a true revival of airing cartoons, and particularly golden age cartoons, across the broader TV landscape the way they used to, especially via OTA broadcast. Packages of classic theatrical cartoons were part and parcel of broadcast TV for about 50 years, but have been almost entirely MIA for 20+ years until this weekend's MeTV cartoon broadcasts. So I'm just rambling about what the future could hold if MeTV were to somehow start a trend in broadcasting.
First and foremost there is MeTV, where all of this is actually happening, and in a lot of ways it is as much and more than anyone could have dreamed of happening. MeTV clearly has a relationship with Warner Bros for classic TV and now animation, based on the Flintstones beginning airing this past year and now the daily Toon In With Me and Saturday morning cartoons blocks. This has given them apparently broad access to probably the largest and best classic animation library by far, and they are taking pretty good advantage of it as evidenced by the two Toon In kick-off broadcasts and the first Saturday morning line-up. MeTV is doing what even Boomerang wouldn't do for years, airing B&W cartoons, mixing in more MGM and Tex Avery catalog with Tom and Jerry, and they are even willing to expand on Popeye with PD Paramount entries featuring Betty Boop. One might wonder if they'd be willing to air more classic Fleischer that is PD, perhaps mainly some of the Color Classics or Screen Songs, although the condition of available versions is likely to be an issue. For Popeye one would expect to see most of the previously restored B&W Fleischer cartoons and perhaps most of the Famous entries as they get restored. Available restored LT/MM material is already deep, but hopefully some unreleased gems will also make their appearance via MeTV's broadcasts. As discussed elsewhere Looney Tunes have been "off the air" for over 20 years. Even CN and Boomerang mostly stopped airing them in the early 2000s, with only sporadic comebacks or marathons (while airing T&J to death mind you), and eventually CN itself had no classic animation of any kind. A staple of ABC Saturday morning broadcasts for decades, the post-49 LT cartoons were last seen there in 2000. The pre-49 package aired for years on local broadcast TV stations and finally in various blocks on TNT/TBS/CN Turner networks through the late 90s at least. Except for briefly on Nickelodeon and CN primarily in the 90s B&W cartoons haven't been aired much at all since the 70s probably, so their unabashed return to OTA broadcast is also significant.
One remaining possibility for MeTV is the other massive branch of WB's classic animation library, the HB/RS/Filmation catalogs. This strays from classic theatrical animation of course, but most people here are interested in some of this material. Now, MeTV is a classic TV network , not a classic cartoon network - so they're not going to become 1990s Cartoon Network. However, considering that most of the broadcast industry has limited or totally eschewed animation over the past 20+ years, its pretty amazing when you think about it that MeTV is dedicating 8 hours a week to classic cartoons going forward. And if you include The Flintstones I think that's another 7 hours or more, for about 15 hours a week of animation. And this has been driven largely by MeTV listening to their viewers. Anyway, regarding the TV animation stuff I think it's likely MeTV would only be interested in perhaps the pre-'69 HB material. The possible exception might be the Scooby-Doo stuff (which you either enjoy or cringe at), but that's still a pretty active old franchise for WB, so it's not clear if they'd be willing to deal on that material. Still, one would think the added exposure at least for the early/classic SD series couldn't hurt. But could one dare to hope to see the likes of Yogi, Huck and Quickdraw McGraw airing on MeTV? Physical media release of much of this material has been encumbered for years with silly contractual rights technicalities, but broadcast seems to not have all these same issues. Condition of available elements for some of the most-requested series may still be an issue though. Already restored/released stuff like Jonny Quest or The Jetsons seem like good possibilities. That aside, like I said MeTV is not going to morph into old Cartoon Network. But it seems conceivable that they could dedicate a rotating hour or two perhaps on Sunday mornings to a selection of classic HB shows. They are actually already doing this with the Flintstones anyway. Flintstones was one of the few HB efforts designed and with production values for prime time, so it was a good fit, but a Sunday morning rotation could definitely support more of the library for a little variety.
That's my commentary and speculation on what is happening now with MeTV, but they have several competitors in the diginet space, some who have actually broadcast or dabbled in animation in the past few years and could conceivably do so again, especially if MeTV's efforts are seen as popular and successful. To my knowledge the most likely competing broadcast alternatives for airing cartoons would include AntennaTV, getTV, Cozi TV, This TV, Movies!, and maybe a half dozen other less likely diginets. The old major 3-letter broadcast networks will almost certainly never regularly broadcast classic cartoons (or much vintage content of any kind) again. A couple of the smaller ones (MyTV, CW) have some legacy or history with animation in general, but I don't really expect much from them either.
So what cartoon libraries could these other small networks end up airing if they tried to do so? I'm going to assume at this point that MeTV pretty much has dibs or has locked up the WB library in this space. Maybe that's not true, but I'll go with that for now.
The most likely alternative library to air on broadcast TV is the Columbia cartoon library held by Sony, consisting of the Color Rhapsodies/Screen Gems and UPA material. Indeed much of it, including most of the UPA material, is represented in the Totally Tooned In! package program which Antenna TV actually aired regularly for the first 3-4 years of the network's existence. If these cartoons do return it would likely only be in the form of this show, and most likely on AntennaTV or another Sony-owned network. The package does generally work okay, with the UPA cartoons carrying the show while allowing room for some of the older/obscure Columbia cartoons with more of a classic golden age full animation vibe. Sony is one of the better stewards of their library, having actively restored and maintained much or all of the Columbia library, including their animated cartoons and Three Stooges and other short subjects. Related to the UPA portion of this library were the old UPA TV series for Magoo and McBoingBoing, but I think they may have different ownership.
The second most likely theatrical cartoon library that could potentially air in my opinion is a toss up between DFE and Universal.
DFE, primarily Pink Panther, Inspector and Ant & Aardvark, has a long history in package syndication and Saturday mornings. The library has been "active" recently in the sense that Olive Films licensed it extensively and produced remastered blu-ray releases of most of it. I think that effort has petered out, but was surprisingly exhaustive and deep. I also think that some Pink Panther cartoons were airing on ThisTV in either a regular block or between movies in the past decade. I don't watch the network much, so I'm not sure if they still do or not. A few of the various DePatie-Freleng 70s series are bland stinkers, but the catalog is certainly large enough to support a weekly or even a daily block of entertaining cartoons. Golden Age they really are not, but they did keep the old production of theatrical short subject cartoons going the longest it seems.
Universal/Lantz cartoons really haven't been seen much via OTA or even on cable in decades AFAIK. But there is some hint of life in Universal animation. Subsequent to their New Woody Woodpecker series of the late 90s they seem to be producing a similar series of new Woody Woodpecker "webisode" cartoons again, shown primarily online via their Youtube channel. That channel also releases episodes of the 90s series and even classic Woody Woodpecker cartoons, primarily the older half of the Woody and Friends library (40s-50s) that was remastered for DVD about a dozen years ago. The latter half of the library (60s-70s cartoons often maligned as the Paul Smith junk, although much of it is still entertaining) has shown up in recent years as internationally recorded bootlegs that actually look pretty good in most cases. All of these cartoons were last running in the US in the old Program Exchange package through the late 80s or early 90s, which were slightly dingy old tape masters, and the bootlegs look marginally improved or at least no worse, so the total Woody Woodpecker library seems like it is in decent enough shape for broadcast at any time. I don't think any of it has every really been "restored" in the proper sense of the word, but they're not in horrible condition. The broader/older Lantz library, outside a few characters like Andy Panda, Chilly Willie or maybe Inspector Willoughby, would be in more dubious/unknown condition. Other than a few remastered entries for DVD the older Oswalds, Swing Symphonies, one-offs and older B&W cartoons would fall into this category and likely never be included in a contemporary package for broadcast anyway.
Then there's what remains of the Fleischer/Paramount library. Much of it, though not all, is public domain, but Paramount owns the original elements. They've shown little interest in this material. Olive Films somehow licensed and has/had access to it for home video, resulting in some decent releases of earlier Betty Boop cartoons. A lot of the rest of this material, while good, is probably considered too old or "not funny", with few recurring or well-recognized characters, and may be of little interest for broadcast, however much we might like to see it.
Related to this library and probably more accessible is the Harveytoons/Famous library. Through ClassicMedia sale to DreamWorks these are seemingly owned by NBCUniversal now. While Classic Media did a lot to release this library (rather imperfectly) on disc, I don't think much has been happening with it since the acquisition, although character use and licensing certainly continues. As to the cartoons themselves its questionable if they could be had in any format other than the edited Harveytoons Show compilation program. I don't know if they'd really be considered restored, but they are in good condition for broadcast. Presumably a broadcaster would go to the same source for either Harveytoons or the Lantz library, so the likelihood of this material airing again may be on par with or even exceed that of the Lantz library.
Obviously Disney classic shorts have never been widely available outside of Disney-controlled media and channels. The past few years I think Leonard Maltin has been able to host a small few of them occasionally on TCM, but at this point they only seem destined for Disney+, where I believe they remain largely incomplete. HD home video release never really materialized either, with a few limited exceptions like the Celebrating Mickey blu-ray. Those that are on Disney+ or will eventually appear there will be HD, but I'm not clear if they'll be unedited. Suffice it to say, I don't think anybody expects this library playing on some low-rent broadcast network at any time.
Probably the most dormant library for decades now is the Terrytoons library, consisting of silent and sound random cat, mouse and farm animal cartoons of the late 20s-30s (similar to Aesop's Fables), the 40s-50s character series including Mighty Mouse, Heckle & Jeckle, Gandy Goose and others, and the later Deitch and Bakshi cartoons. Originally produced for distribution by 20th Century Fox Studios, Terry sold the studio to CBS in the 50s. The ownership has meandered slightly through the years but have effectively landed with Paramount and CBS Television Distribution. There have been only a few abortive attempts to revive the characters, with only Deitch's 1980s Mighty Mouse The New Adventures succeeding and surprisingly being released to disc by CBS a few years ago. It's unclear to me what condition any available materials and elements for the classic Terry cartoons are in. Some prints of them are passed around among collectors, often in rough shape. The originals may be in need of restoration, and such restoration may remain unlikely. Given Paramount's ownership and general lack of interest in their classic animation properties. The situation is only marginally better than if the cartoons had somehow gone to Fox and ultimately to Disney with their purchase of 20th Century Fox studios, as certain things once Disney gets their fangs in them by acquisition are as good as dead and buried. Regardless I think we are unlikely to see these on TV again any time soon, if ever. I'm probably at the tail end of the last generation (gen 😵 to have had much exposure to or memory of these cartoons. Mighty Mouse seems to still have some cultural visibility, but I last remember seeing them air in syndication packages on local broadcast stations in the mid-80s alongside old "a.a.p." packages and Three Stooges shorts. Millennials and younger are probably almost wholly ignorant of these cartoons. They were never the best cartoons, but they were competently churned out most of the time and they have their moments.
Then there's the rest. The classic theatrical cartoon leavin's. We're talking Iwerks, Van Beuren, some Mintz, old independently produced cartoons, old silent cartoon libraries with sound and effects added, mostly 20s and 30s stuff, and then the few PD entries from some of the likes of Famous or Lantz. Some of this, like the PD Famous color Popeye cartoons, has actually aired between films on the Movies! network in recent years. The rest of this material was common fodder in the earliest TV era of the 40s-50s and maybe lasted on TV in some form through the 1970s, but would likely be of no interest to broadcasters today. A lot of it has been PD and commonly available in compilations for years, though some of it is officially or nominally owned by the likes of Blackhawk Films. The simple reality is that almost anything older than the 1940s or very late 1930s, with the exception of Popeye, Disney shorts and maybe Betty Boop, is of no general interest for airing on TV today.
To sum up, I think MeTV has a lock and some possibilities going forward to broadcast LT/MM, T&J/MGM, Popeye et al, and maybe some more HB series. Hopefully they see a lot of success with it. One of the Sony diginets could bring back Columbia/UPA, most likely as TTI. If there are other networks interested in showing classic cartoons then I think the DFE, Universal/Lantz and Harveytoons libraries retain at least athe possibility of returning to air and still have popular/recognizable characters. The rest all seem very unlikely to me.