Not much on Atumbel over the years, but the Wiki says citing the Unapproachable East vok from 3.5:
"While many outsiders failed to make the distinction, the Altumbellan people saw themselves as a prominent nation separate from their neighbor Aglarond."
So as a nation, it is botb a minor note and primarily defined by being "we are not with these weird Sorcerer-followers over there..."
Well, as one of the 10 regions that gets a Background, I guess something like "Bedine Nomad" is a major PC concept. Lots of room for adventure ture there, too.
Yeah, I am sure there will be a Beyond section that gives a little bit about the South of Faerûn, and probably Kara-Tur etc.