I honestly think they could confidently release at least Zendikar, New Phyrexia/Mirrordin, Kaladesh, and Alara. That's 8 years of gameplay since they don't release a Magic setting every year.
If they want to go the way of TSR they could do that. Only Zendikar would definitely sell well, and 5E would have massively overstayed its welcome by then, and the systems it uses, which looked relatively modern in a slight retro way, in 2014, by 2029 will be looking positively ancient. You'd definitely see a steady decline in sales over that period if you were spamming MtG settings like that and not innovating D&D. You might even see a scenario like that of 2E, where people actually started to move on to other RPGs, because D&D seemed so stuck in the mud. I think it's less likely now but not impossible, and if that happens, getting them back with a 6E after they've tasted various forbidden fruit re: mechanics and general game approaches will be considerably harder.
Yet still WotC's numbers showed there was overwhelming satisfaction with thebRangee...even if less overwhelming than other Classes. That's the issue, they are trying to please a majority, not the vocal customers. That takes time and consideration.
I don't dispute the facts, but I would suggest this "majoritarian" approach has failed them. Further, it looks like an early-5E approach. You'll notice the time between UA and stuff going in a product has, by and large shortened considerably, and we're seeing a hell of a lot less feedback from WotC on our playtesting. This, I would suggest, is because they've become more confident, and their UAs are now to catch outliers (i.e. in the sense that something that sounded good to them sounds really bad) and correct balance issues they didn't previously notice, rather than to match the old majoritarian 70% approval magic number.
The old approach cost them the Mystic, which had they just ignored the 70% approval thing would inevitably have been accepted in within 1-2 years (it's just the way D&D goes), outside some hardcore minority who are probably still made about Artificers right now. And I suspect it cost them other stuff which would actually have worked fine.
You can have "satisfaction" with a class and it can still be total crap, frankly, mechanically. I mean, if you read D&D boards it's obvious about 75% of D&D player don't understand mechanics beyond the most completely superficial level. That's not a huge problem. You don't need to understand D&D in depth to play or run it, or even apply simple house rules. But I would say certainly the majority of D&D players are outright
incapable of understanding mechanical issues in any depth, let alone ones which might seem more subtle, like with the Ranger. There's also the oppose change crew, who would rather have a mediocre or bad ranger than a new ranger - a small but present minority.
This isn't an issue unique to D&D. People are broadly satisfied with all sorts of dreadful systems, it's something I see in my work. When you replace a system, though, people can be shocked and overjoyed, they didn't even know something
could work this well.
Back on people not understanding, you could see this very often when people attempted to discuss UAs on the reddit especially (the level of technical competence and understanding is significantly higher here but we still see people who are really grasping what is going on mechanically wading into nuanced conversations - ones re: the Monk are particularly hilarious because the same people wade in with the same irrelevant points and are shocked when they're largely ignored), because it was the blind leading the blind, frankly. Entire thread with dozens of comments and hundreds of upvotes featured people who'd made basic mathematical or rules errors, yet everyone was going along with them.
Hence my suggestion that majoritarian approaches are of limited utility unless all you're trying to find out if something is so incredibly bad it needs to be changed
right now. If you want to actually find out if something needs changed, you need to ask the people who are saying it's bad and see if they have any kind of rational argument at all. Often they won't. But sometimes they will.
And I don't think current-WotC is going with this groupthink approach anymore. I don't think we'd have seen Tashas or half the changes in it if they were. People were already "satisfied" with virtually everything Tashas changes or adds to. But they're more satisfied now, I'm sure.
This whole thing goes back to 5E being an "apology edition". 5E was born because bad decisions around 4E split the community and lost WotC a fair fraction of their playerbase. 5E was an attempt to win them back and provide a more future-proof game, but it was very consciously trying not to offend (unlike 4E). That's why the approval threshold for material was both public, and so extremely high. WotC was afraid. WotC wanted you to know it was only doing what you asked it to! Not any crazy 4E stuff!
But given persistent year-on-year growth from NEW players who utterly dwarf the old players in numbers, that is no longer a real problem. WotC has become confident. Theros. Tashas. Candlekeep. Ravenloft. These are the books of a confident company. Not a company nearly-groveling for approval. The recent UAs have been bold too. I don't think Rabbit and Owl people would have been seen as okay to even put in a UA in 2015. In 2021? People are excited by that.
So I don't think this "please a majority" thing is as simple as it once was. With an audience so large, even if a book isn't for everyone, it's likely selling more copies than a book that was for everyone did in 2015.