The catch being, WotC really wants every book to be a must-buy. If people know that in 2-3 years there'll be a new setting, then they're not going to buy the FR book now. And if they already bought the FR book, they're not going to buy the new setting. And it's potentially confusing for new players, possibly making them ask "is this the same game?"
I don't think there is such a thing as a "must-buy," except for the PHB. The DMG and MM are almost must-buys, but only to DMs. And so it declines from there in a curve. It seems that with 5E, WotC has decided to cut things off at a very "fat" part of the curve, at least relative to past editions, although to be honest I wonder how the story arcs are selling relative to setting books or splats.
Even if they release a new setting every 2 years, it will take a long time to go everywhere. There are a good dozen campaign settings. Are you really going to be happy waiting 24 years for your setting of choice?
And not every setting *needs* an update. You can run an Eberron game using the rules pamphlet and a 3e or 4e book. Literally nothing has changed in the world. The market for settings is awkward because you're selling to non-fans (who don't care and/or already have a setting they like) and fans (who have books from previous editions). A Greyhawk fan already has the Greyhawk material, otherwise they wouldn't be a fan. They have more content then you can fit in a single book. And the mechanics for Greyhawk haven't changed.
WotC's current strategy seems solid: focus on the Realms. That world has changed and needs an update, and they need to release at least one setting product for new players.
Other settings can benefit from the Eberron approach, where we get a document of essential races and classes. Pair that with DnDclassics.com and we have all the content we need. We don't need new Dragonlance books, we need a PDF with kender, draconians, primal sorcerers, and moon magic, then make the classic products and the licenced 3e books available as PDFs.
At best WotC can expand on the Realms. Kara Tur and Al Qadim sourcebooks would be neat and offer opportunities for new stories while still remaining in the Realms.
OK, it is hard to disagree with you here. Given what you say, I could see a Realms book, one or two supplements, and then maybe a new setting. But as I've argued for years now, I think one of the reasons 4E suffered is that it didn't have a living world like Golarion to tie it together, to unite the community. Maybe the Realms can be that, but I think they can--and should--diversify a bit. At least eventually. In a few years people will be ready for something new.
The problem with a setting, overall, is that it is a niche-of-a-niche product. If you write a Dark Sun product... only those who like and play in Dark Sun are going to use it. For a game like D&D, that traditionally supports multiple settings, developing a product on a particular setting is developing a product that you *know*, from the outset, is only going to be attractive to some smallish segment of the overall player base. The payback on that development is going to be limited.
So, you wind up considering opportunity-cost - with the same creative resources, can you create something that more people will buy and use? If so, then it pays both you, and likely the game, to do that other product.
Yes, true, but everything is a niche product - or at least down the line in the "product tree" from the PHB. As I said to Jester, the question is where WotC chooses to cut things off in terms of diminishing returns on product - "nicheness."
One thing to consider, though, is that Paizo has produced a fairly comprehensive edition in Pathfinder, not dissimilar to 4E or 3E, although with a focus more on adventures and "mega-splats" rather than yet another "Complete This or That." So it must be profitable enough for Paizo to stay the course, at least so far - six years in their cycle - and with no sign of slowing or veering. It seems that the powers-that-be at WotC have decided that they need a higher profit margin, or at least a much slower roll-out - which may be good for Hasbro, but is not so good for 5E fans. I mean, don't you want a 5E
Manual of the Planes? A living setting? An
Unearthed Arcana once in awhile?
It doesn't have to be all (2E, 3E, 4E) or almost nothing (5E) in terms of product support. There's a middle ground possible, that would feed the game.
I'm not giving up hope, mind you, and think we could have surprises in store for us. But I do harbor a fear that what we've seen so far is all that we're going to get, which as a fan of the game would be quite disappointing.
Absolutely that's what they want.
But what after the PHB, MM, and DMG do folks consider to be "must buy" D&D books?
Nothing is a "must buy." As I said above, it is a curve of diminishing returns. The question all publishers must ask is where to draw the line. Clearly WotC is choosing to draw the line when the curve is still quite thick, at least so far. We can hope that they stretch it out a bit.
Yes, it is the big question.
I'm not sure if even WotC's marketing gurus know. Or maybe their conclusions was "nothing is a must buy after the core 3", and that's one of the reasons they're pursuing multimedia.
You think one big accessory per year would be a "must buy"? Something like a Monster Manual 2, Manual of the Planes, or Dungeoneer's Survival Guide?
I wonder if, given their small crew, commitment to book quality/size, and the multimedia innitiative, they have the time & resources to produce such a book in addition to their adventure books?
Or maybe they've got things lined up so that their accessory books line up with whatever storyline they have in mind? So release MM2 during, say, the Alice in Wonderland/Dungeonland inspired storyline, taking advantage of the new fey/weird monsters in MM2 to tell their story.
As I said above, it doesn't have to be all or almost-nothing. There are countless variations between 2E-to-4E style glut and 5E minimalism.
I think a good middle ground would be something like this as far as yearly out-put goes:
One big splat expansion book - a Manual of the Planes, MM2, Fiend Folio, Unearthed Arcana, etc
Two story arcs (as is)
Several short adventures
One setting book
That's maybe 6-8 products a year. Paizo publishes less than that and is not just surviving, but thriving.