Agreed, that's why I said "anything reasonably popular".
Universes Beyond (abbreviated as UB[1]) is a “sub-brand” of Magic: The Gathering that exists in addition to, and alongside, the regular line of products.[2] Not unlike the original Deckmaster concept, Universes Beyond is a series that combines the gameplay of Magic: The Gathering with worlds...
mtg.fandom.com
Universes Beyond is a bit of a sore spot with MtG fans at the moment - while potentially not the cause, the sharp uptick in UB stuff (which is going from "zero sets in standard" to "half of all sets released into standard" this year) dovetails with a perceived decline in the care and attention put into the actual MtG IP. There are some bright spots but there are also a lot of really clunky messes, too. The most recent set is... looking like one of the clunkier and messier.
Interestingly, the Forgotten Realms MtG set was
not considered UB - it slots in seamlessly with MtG, despite canonically the D&D and MtG multiverses still being separate. I've been somewhat under the impression that MtG stuff has been treated similarly in D&D spaces - I see plenty of people who like the Ravnica or Strixhaven stuff, for example. Ravnica's one of my favorite fantasy settings in general. I see fewer fans of the Theros book but they're out there.
Thankfully, I don't think we'll see anything like "half of all new adventure and/or setting books are replaced by UB." The incentive to overwhelm the WotC-sourced output with UB stuff is not really there for D&D - much harder to exploit gambling addictions with TTRPG books than with randomized packs of playing cards. You gamble
in the game, not on the products.
...Knock on wood.
I'd expect any UB stuff in D&D to fall somewhat into a splat/setting hybrid category, possibly with included brief adventure modules. I don't see it being feasible to split that over multiple books for how briefly they're likely to engage with one UB crossover at a time. It'd probably look like the Magic books in being relatively standalone and self-contained. How well that would translate to stuff people will enjoy... idunno. MtG has the benefit of every D&D class and many playable species slotting almost seamlessly into basically any of its planes - UB settings may struggle with that compatibility.
rehashing Xanathar and Tasha
Maybe this'll make me look silly in the future, but I think a rehash may end up combining the two - a bit like MotM did for Volo's and MToF. I actually kind of hope they do something like this.
Naturally, the word "Everything" must appear in the title. Now, would it be "Xanathar's Tasha to Everything," or "Tasha's Xanathar of Everything"...? Perhaps "Xanathar & Tasha's Guide to Cauldroning Everything?"
...Maybe I look silly already.