The 3e FRCS is certainly usable, but then again so are the guides to all other settings from previous editions as well.
But this is a well-worn road to a discussion that has been done and re-done here ad nauseum.
Basically, all Realms fans want is to see the rest of the setting get some coverage. This is fine if it's done via a new setting book, or by placing hardcover adventures in new regions like was done with Chult, or by having Ed and other Realms experts create "semi-official" books on the DMs Guild like what was done for the Border Kingdoms. Any of these three are fine. They just need to choose one (and indicate that choice to us so we know what to expect) and go with it.
Well, M. T. Black is doing more products in conjunction with Ed Greenwood.
Honestly, they are opaque to avoid overpromiaing: if they say "we're doing X now," and conditions change...a lot of people would be upset that X stopped.