While I certainly wouldn't mind going to Atmora, I thought it wasn't so much missing as frozen solid?
Even with that being true there are still possibilities of course. Lots of ancient ruins buried in the ice, the mystery of how/why it froze over in the first place, settlers and explorers who are in way over their heads and need the player's help to obtain food/find shelter/fight off thegiant Ice Worm with the huge burning knife for a facenative creatures. Entire lost cities populated with the ghosts of the people who didn't flee to Tamriel in time...officials getting assassinated left, right and center as the various factions try to outmaneuver each other in order to lay claim to it...