And a third- a vampire realm of some kind, an alternate dimension.
Yes. Maybe the afterlife for vampires, since we see dead souls in the trailer. And he mentions feeding on souls of both the living and the dead.
My theory of how you join the vampires
Basically, I think it was Molag Bal voicing the trailer. And we all know Molag Bal created vampires when he [censored] some woman. In the trailer he says 'you have returned to my daughter'. Could this mean we meet one of his vampire daughters, who leads us to their lair?
Maybe not. We see Molag's symbol on a bleeding shrine and the Vampire Lord's armor. And Molag had a daughter called Molag Grunda, but I doubt it will be Molag Bal.