Goblin Queen (She/Her/Hers)
If I could, I would vote for a combination of options 4 and 5. Their publishing model for 5e seems to be to bundle a bunch of player, DM, and fluff content together in a book built around a common theme. Even Xanathar’s, the closest thing we’ve gotten to a “player’s guide” this edition followed the model, it just has a flimsier theme than Volo’s or Mordenkainen’s. My money is on another one of this style of book, with the unifying theme being interplanar travel, that will serve as a low-key Planescape setting guide. “Elminster’s Guide to the Planes” or something like that.