This, we can agree on. I don't necessarily mind if a dlc has to do with a daedric prince, like Bloodmoon did. And in all honesty, I wouldn't mind seeing Solstheim again. I know a lot of people would be against that though and I can understand why.
Why wouldn't people want to see it again (no sarcasm I don't know the reasons

) ? I mean lots of people wanted to see morrowind and oblivion revamped (haha i'm the king of puns)
To Montblanc I see your point on how expeditions to atmora have not found anything but remember that Atmora is very large and is infact a continent in itself, so I doubt all of Atmora was explored, and if you were fleeing a large race of genocidal brutes and you werery hiding quite close to their country I'd go as far as i could from there so they probably went very far north and I they might have been able to survive there for a while until they adapted to the hard conditions and it would be easier for them to adapt to the extreme conditions seeing as they lived in skyrim so they could probably last longer than most other tamrielic races. Plus seeing as the Dwemer could live underground and survive quite easily underground so snow elves could probably survive just as well seeing as they would be more advanced than early dwemer when they went underground. Plus they could survive under there for a long time slowly bolstering there forces until they could find a way to easily survive on the surface. Also if a snow elf like arch curate vryther could change a prophecy from an elder scroll I think they could probably find a way to heat up a small area of atmora with magic.
Well your explanations could be valuable I mean there's always a way to get around the lore since there almost isn't any about Atmora ! But how could we explain that the falmer split up , one group seeking help from the Dwemer and one leaving the province ? The Nords were decimating their ranks it didn't seem like they had any choice but to depend on the dwarves ! Woud they have struck such a terrible deal if they had known they could just sail off like that ?