My theory of the Snow Elves involvement: maybe they're gonna appear as a playable race of elves, have something to do w/ the vampires, or are for some quest.

My theory is the falmer will join the Vampires as I would think they would like the sun being blocked out.

I doubt the Falmer would become a playable race this late, and even then, I recall hearing that they believed ten races were sufficient enough.

I think if they play a roll anywhere, they'll either be Cannon Fodder troops if there's a battle, or the vampires themselves will be an evolved version of the Snow Elves that embraced vampirism to combat the Nords. Having become immortal lords, time will have flown by and it will be only now they muster the confidence to attack.

I think the snowprince dying was all a hoax cause there sure wasnt a skeleton with that armor in morrowind. I think the guards were posted at the burial mound so that none found out. And that he is hiding biding his time and will rise up and rule the falmer once more...or there could just be dead ones in the soulcairn