This is quite the world you are creating, I look forward to reading this if you ever get it started.
What happens to the Dunmer in this world? I can see them getting boosted due to their mer blood but they are not allies to the Dominion, so would they be some kind of middle-class citizen below the Altmer and Bosmer but above the humans and beast races?
When you get around to plot, I have to say I'd like to see a lot of controversy not only between the people of Skyrim and the invading Dominion but also between parts of the Dominion itself. What do the Altmer leaders think of their Bosmer allies, now that they have near supreme control over Tamriel? Will they turn their backs on their allies and start forcing them to conform to the belief of specifically Altmer superiority, not just the superiority of anyone of merish descent.
I can see much strife coming from the differences in religion within the Dominion itself, too. There are still Altmer who worship their traditional pantheon (Magnus, Phynaster, etc), and those who worship the Eight Divines, not to mention the Bosmer's probably blasphemous Green Pact.
It would also be interesting to have one point of view from an elvish mole within the Dominion, relaying out of the inner confines of the Dominon. Maybe what happens if they get caught (killed, obviously), but what would happen to the people on the receiving side of the info? Would they search for a new contact or not?
Hope this stuff helps with your ideas. Again, I really look forward to this if you ever start writing it.