Not sure how Vampires would tie in with that one, maybe they would fit in better with the events of red moutain.
That's the one real problem I have with vampires as the main focus of a DLC.
I'm afraid that it might seem forced, because their appearance in Skyrim seems almost like an afterthought. I can not remember a single interesting quest that included vampires and the only vampire that I thought was cool is Babette (and my own). Vampires had about as much impact on the game as a cotton ball thrown by a baby - absolutely none. It was nice that they were included but they weren't needed for anything, and becoming one was something I did for the lulz.
So far, we've got practically no story that a dlc could expand upon, not even interesting hints, just lore established prior to Skyrim, so they'd have to start practically from scratch to make it work.
I just hope that they don't do something stupid in an attempt to please everyone. Something like 'oh, we forgot to mention this but the Falmer are actually vampires, and the snow prince is a vampire lord and just tricked the nord, he never died, sorry we didn't tell you earlier, it was supposed to be a surprise'. That'd ruin both vampires and snow elves for me. My personal worst case scenario.