http://www.uesp.net/wiki/Lore:Atmora
Supposedly, all or most of the human races (except Redguards, who were from Yokuda) originated in Atmora; the Nords, Imperials, and Bretons (who are actually the result of Nedic-Altmer intermarriage), originally one race referred to as Nedes. I'm sure that there are a number of ruins (barrows, towns, forts) that may be left intact. It's unknown up to this point if anybody is still alive over there given the harsh climate (worse than northern Skyrim), but I wouldn't dismiss the possibility of a few hunter-gatherer tribes along the southern coast of the land. One thing that I would doubt is any sort of large scale political organization existing there anymore; a kingdom.
I don't think all of Atmora should necessarily have to be included for an expansion pack like this to work, as it's a massive continent I think, but Bethesda could make it relatively easily, given that it seems little different from the far north in Skyrim already (snow and ice terrain, blizzards).

