The dwemer, or dwarves for those unfamiliar, died at the battle of red mountain, with the exception of a few mainly the man in the corpusarium. I do not believe however that there are none left. The first reason being that people adventure so why not hace dwemer traveling across Nirn. Another scenario involving dwemer movement is that they moved for more resources. I think it would be a great expansion or another game if dwemer who were hiding from the battle(women and children) or those who have been traveling return to tamriel.
Think of the possibilities this could offer.
1. Big new event = dawning of the fourth age
2. New technologies, how awesome would it be for a simple railway system. This could work for heists fast travel and well numerous other missions. (also lay down land mines like the ones from tribunal. that would add some interesting gameplay.)
3. Play as a dwemer. A race that is as tall as bosmer, but with intelligence and strength.
This mod could add into morrowind or simply have the dwemer returning all around tamriel. Why not have them build in mines and recover ore and then have a dwemer civilization.
I think this is a great idea and it does seem possible just think of the dwemer form morrowinds main quest.