I would say there is a whole legion of Realms fans who hated the 4th edition changes and are anxiously waiting for a 5th edition FRCG. Especially since the theme now is to bring back the "Old Realms" as much as possible.Sure, I don't disagree with you... my only thought is that it'll tend towards later just so that the stuff they currently have on the docket for the Realms gets published so as to give more stuff to truly change entire book sections. Because while things like the pantheon has seen a HUGE shake up and which impacts the entirety of Faerun in huge ways... the "Deities" section of the campaign guide is but a small section of the book. The re-split of Abeir and Toril will produce huge changes for those half-dozen sections of the map that overlapped in 4E... but in the actual Geography section, that's only six sections out of how many areas to be detailed? And those sections constitute only just how many paragraphs/pages of information? And as far as Organizations are concerned... even in the 3E guide that only encompassed 10 pages of material in a 300 page book. So despite what could have huge ramifications on Faerun as a whole... in the actual book, it would probably only result in a small percentage change as far as page space is concerned.
That's really my only thought. How much of the book sections themselves have seen enough change from the 4E book to warrant the book being produced again? That I couldn't really say. And for the stuff that has changed... what is the best, most efficient, or financially viable way to get that stuff out there? Web enhancement articles? Soft cover small area campaign books that will see changes every year? A full campaign guide? Or relying on those DMs that truly care about "up-to-date" info to actually purchase the products that has seen the changes take place? I don't know what is the right answer... all I know is that WotC does not seem to want to just release "product" for the sake of having product out there. Yeah it sucks for those DMs who want all the official lore combined into a singular form, but I have to imagine that they just don't think it's financially or creatively worthwhile to do at this point in time. Maybe there just isn't enough people out there who would buy the book to warrant spending all that time and resources to put it together?
A thick FRCG and regional web articles is somewhere you can't go wrong.