The Magitech setting for TSR's Amazing Engine RPG said that it could be used for Toril in the far future.
My 3rd edition FR guide still works perfectly well.
As much as I'd love for them to move away from it entirely for at least a while, just to give the other settings some AP love, what I expect to happen is that they'll continue exactly as they have been. It'll remain the default, it'll remain the home of most APs, but there won't likely be a "sourcebook."
Indeed, the last FR game I ran for 5e I set in DR 1372, because there’s just not enough info out there for the realms at large post-4e time jump, whereas for the 3e FR book, I know rulers, I know current threats, I know NPCs, etc. the Sword coast guide only gives me this for a fraction of what the FRCS did. I know tons about the sword coast, but if I want to run in, say waterdeep, or the dalelands, or hillsfar, i’m Out of luck, so back to 1372 I go!
My 3rd edition FR guide still works perfectly well.
My 3rd edition FR guide still works perfectly well.