I think that a DLC regarding either the Thalmor, Falmer, or Dwemer would be the most likely. A war with the Thalmor ties in with the main story, which I feel makes it the most likely candidate for an in-the-near-future DLC. Alternatively, there are books scattered everywhere regarding the Falmer and Dwemer, and tons of hints that the Falmer might rise up, and the Dwemer might return. This, in my eyes, makes it another incredibly likely option for a DLC (and my favorite), perhaps each one happening in two separate DLCs, or in one big one. Maybe the Dwemer come back, but have been altered somehow?
I'd also like to point out (and this is a major, major spoiler) that in the Dawnguard DLC, we find the Unknown Books that are written by ancient Snow Elves and must be translated. In one of those books, there's a suggestion that the Snow Elves may have chosen to become something else - to change, in order to survive. Perhaps they didn't realize what, exactly, they would become (the Falmer, blind and hateful), but in their desperation, made a decision that created their future. And maybe, it didn't involve being force-fed toxic fungi, like everyone believes? I definitely recommend having those books translated and reading them yourself, or looking them up online if you're lazy. hehe The information they contain is definitely open to interpretation, and I could be wrong, but I really hope that the next DLC offers some definitive answers regarding what happened to the Dwemer and the Falmer, and what their future entails.
