We'll find out when 6E lands.
I expect evolution, not revolution though. Backwards compatible maybe.
It'll be heralded. And I bet I know when.
But I agree it will be very backwards compatible. You won't have to change (unless your only play is in the AL), but the improvements will encourage you to do so.
That's all true, but I think it misses the competition in the market. 3.X had the misfortune of being in the marketplace competing against a ton of D20 RPGs (which was, arguably, their own doing) as well as the widespread success of MMOs and collectable minis games (things that couldn't be foreseen), both of which took substantial market share from D&D. As I recall, Monte Cook said that 3.5 came out when it did not because it wasn't part of the overall business plan (it was for a few years later) but because 3.0 sales dove faster than they expected. 2E came out right when two big competitors emerged: The White Wolf games and, way more importantly, CCGs, both of which were certainly unforeseen by TSR management. So, in a lot of ways, the fight for market was a whole lot harder. Of course, one might argue that this doesn't account for why 5E has been so successful... to be clear, I don't know either, but I really don't think that things like live streaming of other people's games would be so popular was something anyone thought of in 2012.
The 50th anniversary would be a logical date, abstractly, but abstractions ≠ market realities. If 5E is still going strong, they won't do a new edition at that time.
Well it's 5 years away, it's a nice number for a new edition and 5E would be 10 years old.
Failing that an anniversary cover
My theory with 3.0 was sales were so front loaded they hit saturation point a lot faster.
3.5 is the second worst selling D&D after OD&D, maybe 4E but I suspect that one sold well initially but cratered fast.
1E, B/X and 5E made a bigger pie.
D&D can't really sustain a 2E to 4E publishing schedule. Prime example if milking the existing fanbase.
I remember the sheer ugliness of some of the hate that 2nd edition got in my neck of the woods. It broke at least one game group apart because half wanted to upgrade and the other half actively despised every single thing about the new edition - from the artwork to the organization to every minor rule change (and if you really wanted to see them mad, get them started on the loss of the assassin or the introduction of the new bard to the game). I hesitate to think of what might have happened had there been any actual rule changes of the magnitude we expect of an edition shift these days.
(I assume they all outgrew it - Junior High Drama is the second stupidest kind of drama, second only to Ostensibly Grown Adults Who Should Know Better Drama, which is the stupidest of all).