I'm always happy for new setting books and I'd buy a new FR setting book if it was purty, but I have to ask: What would people actually expect from it that the classic 3e book didn't already do, except updated stats and player options that were already in SCAG? Meaning, as much as it is fun to get a new setting book, it feels a bit like that second (or third) squeezing of a lemon. Maybe time to slice open new fruit? How about a lime? Or a pineapple or some rambutan?
This endless re-hashing of old setting material--or at least yearning from it, from (I'm guessing) a relative minority of setting-faithful fans--just seems like re-inventing the wheel, again and again. WotC isn't likely to improve upon the FRCS, which is a masterpiece that many consider the best setting book ever made. I for one am rather pleased that they've chosen differently and are branching out into new* settings like Ravnica and Wildemount. I truly hope that the next setting book is Zendikar or Dominaria or maybe the home setting of one of the WotC people. New worlds to explore, and all.
That said, what does make sense is a Planescape or Manual of the Planes book. There's enough edition-specific material that hasn't been covered to not only justify such a product, but to make it almost necessary to easily play a planar game.
(*new for non-Magic players, but still new as D&D settings)