When it comes to huge specualtions with virtually no evidence at all, I like to believe we TES Fans take the gold, so now it's time to do what we're famous for, my idea is..
Dawnguard is in Hammerfell, the remnants of Redguards of the Great War will team up with the rest of the empire.
They will force back the Aldmeri Dominion and form a coalition known as The Dawnguard.
This is just speculation not real info.
What do you think?