I gave this answer in a similar thread, but this thread seems more appropriate. I apologize for the "double-post".
I agree that a true new edition needs to be some kind of major development. 5e still seems like it has a lot of life to me, and has been pointed out, has never been bigger or more successful.
But I don't think the people here are thinking big enough. WotC have already said they want a quickstart D&D where two new players, a character and the DM, can start playing in an hour. Moving in the direction of greater simplicity and player enjoyment has been a winner. 5e is doing something perhaps few other games can do: it is growing by bringing in completely new players who might not play anything else, rather than getting existing players to buy more (which WotC are also doing at the same time).
So let's extrapolate from this:
1) No DM: Eliminating the DM is a huge but inevitable step. Good DMing is very hard and ultimately gets in the way of many players' wishes. To be clear, I strongly dislike this direction but fear it is inevitable. This, of course, will require major playtesting and a very different "engine".
2) Solo play: Another logical conclusion. And solo play will be a huge sales boost. Imagine the number of new players who can play however they want with no judgment whatsoever. It's the closest we could have to a Star Trek holodeck. This would require innovative new approaches to existing tools like procedural generation and programmed modules.
3) Celebrity authors: Just like screen actors have muscled in on voice acting, professional authors may take over writing RPG modules, with former RPG authors reduced to converting the stories of professional authors to the RPG format. Again, not a result I desire at all, but a result that seems likely. This would require tools to "gamify" stories in a consistent D&D manner, with game designers helping the authors.
Combine these 3 developments and you get the perfect vehicle for anyone to be the hero of their own personal story, with no one to say they're doing it wrong. And of course, you will still be able to play with a DM and multiple players. This strategy is purely additive in bringing in players who would otherwise never give D&D a look.
Are these developments likely? Probably not, and certainly not soon. But the key is they are answers to the question: "How do we sell D&D to people who currently do not play?" And they might conclude that, nope, DM-less play can't be done. But D&D is now a growth property for Hasbro, and I guarantee that the number crunchers will ask these questions of WotC (FWIW, I have an actual financial background and experience in dealing with publicly-traded stock companies, though I have no personal knowledge of Hasbro or WofC).
P.S. I'm actually a 1e player and wargamer to boot (aging, indeed). So none of this analysis reflects what I personally want to see.