Urriak Uruk
Gaming is fun, and fun is for everyone
Now that we have seen the Icewind Dale announcement, but nothing else teased at all, except for the vague comments in their diversity announcement, it is time to bump this back to the top and get speculating again.
Very well... I guess the Q4 book is another Volo's Guide/Xanathar's style book, with a mix of new racial options, class options, and monster statblocks. Not quite a new player's Xanathar's and not quite a monster book of Volo's, but something in-between.
I'll give it a planescape theme as well, though I don't really think it's an actual setting book (though i guess it could be).