Durpar is tucked away at the very southeastern corner of the continent, so it's been overlooked before (even in SCAG, where just about everything else at least got a mention). However, it is a pretty large region, along with its neighbors Estagund and Var the Golden, all of which have a similar "Durpari" culture from when Durpar ruled the region. It would likely at least garner some mention in a prospective 5e FRCS, although if that's a paragraph or a full entry is anyone's guess...No offense, but that doesn't sound like a nation worth creating (for 3E?) or detailing for 5E. Fold that into another nation at most.
The notion that every concept that's ever flown out of Greenwood's fingertips needs to be memorialized and carried forward into every edition of the game isn't a great one. At some point, the setting gets painted into a corner, which I suspect is partly why WotC had the weird 4E panic attack about the setting that it did.
Better to either detail the areas that have the most value in them or push out beyond the horizon to new areas that have never been created.