As much as I would love them to redo the 3e FRCS for 5e, I'd also love it if they'd do more mini-gazetteers like the ones that came with Legacy of the Crystal Shard (for Icewind Dale) and Murder in Baldur's Gate (for Baldur's Gate). The latter got re-updated in Baldur's Gate: Descent into Avernus, and parts of the former were included in Storm King's Thunder. I really liked those products and would have liked to see more of them.
That said, this year I'm going to be running the Greek-inspired Odyssey of the Dragonlords for one of my groups, and I am hoping to finish up SKT and maybe move on to ToA (without the death curse) for my other group, so I don't particularly need any more FR content. It would just be nice / fun to read.
I'd also be happy with a 5e Dark Sun setting book. Don't particularly care for Greyhawk or Spelljammer. Planescape would be OK but otherwise I'd prefer a brand new setting. (MtG planes as D&D worlds don't count, in that respect.)