A DLC where we learn what happened with the Dwemer by using the elder scroll as time travel.
Which should then only be available after the main quest line is complete... also allow us to help the Falmer/Snow Elves if we do have time travel.
Maybe a DLC with the mystic psijic order?
I was looking forward to raiding the Oblivion realms in Skyrim or the Skyrim equivalent of Daedric realms, but adding it now would probably add a lot of complexity towards Dragons and Daedra interaction. Maybe an all out Dragon vs. Daedra war in an oblivion realm where you control and fight for one side or the other...

love the dragon/daedra war and your able to pick sides and theres a general for each side and he has liutenants like molag bal and mehrunes being joint generals and hircine being covert ops amd harmaes mora the tactician, and there all in there true horrible forms of ultimate power like some huge fully fledged war

I would love to see the Falmer rise up and fight against Nords and the various peoples