I'm thinking four books a year, roughly one a fiscal Quarter, is what WotC is aiming for these days. Crawford did say on Twitter last month that they were just finishing the next hardcover before Christmas break, so we'll see something soon at any rate.
My pulled from thin air predictions:
- Q1: A new Monster book, or an old Adventure compilation
- Q2: Bit of a wild card (pun intended, I am so sorry), but I expect a Magic: the Gathering Forgotten Realms tie in of some sort, a full FRCG tying into the cards coming to M:tG.
- Q3: A new storyline. Haven't really been tracking Dragon Talk lately, so dunno if any clues are current, but I'll go with Neverwinter or the Moonshae Isles as the microsetting.
- Q4: Innistrad Campaign Setting.
I'm going to jump on this comment, because there's a lot I agree with here, and a little I don't agree with.
Q1: Definitely agree it will either be a Monster Book, or an Adventure Compilation.
Q2: IF Q1 was the Monster book, Q2 will be the Adventure Compilation (or reverse).
Q3: New storyline. Still thing Lantan/Spelljammer is a strong possibility (and I hope it's what is happening) but could just as easily be anything else.
Q4: Legacy Campaign Setting, either Dark Sun, Ravenloft (with maybe some Innistrad tied in), or Dragonlance.
Monster book, specifically a 5E Dragonomicon (it may have an entirely different name, but a Volo's style book themed around dragons) seems like a no-brainer. The monster books sell very well, and there hasn't been one in a while. Dragon material is being teased in recent UA, and Gem Dragon statblocks have been teased last year. So this seems like one of the "definitely happening" for 2021.
Adventure Compilation; not old adventures, but original adventures collected from various DMsGuild and other D&D-adjacent people. Kate Welch teased this a while ago, and although I thought it may be shelved, it was again teased in one of last year's streams (I can't remember which one, but it was very much a confirmation it was still happening). So this seems like another "definitely happening" for 2021.
Not going to speculate too much on the adventure, other than hints at Lantan that haven't yet materialized. Lantan seems like a great jump-off point to Spelljammer, but that's just my optimism.
And lastly, a Legacy Setting. Again in last year's stream, they teased that more settings are coming, including old ones. And I think since the last setting released was Theros, WotC will maintain their pattern of now releasing a Legacy one (Ravnica, Eberron, Theros, etc.) The most popular of these that haven't been released are Dark Sun and Ravenloft, but with all the Dragonlance stuff swirling, it is a possibility as well.