I came to this conclusion while I was looking up the different vampire clans from TES lore, I found out that the strongest vampire clan the Volkihar actually live in eastern Skyrim; possibly near Falkreath located is southeastern Skyrim near where the journalist from the article says he was adventuring when he discovered the door.
The Volkihar description kind of ties in with the area around the black door that the journalist was describing in his article.
Volkihar description: "The Volkihar are paranoid and cruel, whose very breath could freeze their victims' blood in the veins. They lived beneath the ice of remote and haunted lakes, never venturing into the world of men except to feed. They also have the ability to reach through the ice of their lakes without breaking it."
Journalist's description of the area near the door: "Take for example the black door adorned with a skull I found near a frigid pond in a rocky recess." (but what does he mean by frigid pond, how can you tell if an in game pond is frigid? was it frozen? Could it have to deal with the ice lakes the Volkihar legends talk about?) Than he goes onto say "The door spoke to me in an otherworldly whisper while shimmering faintly, and asked if I knew the music of life." (the door is asking the player if they know the music of life, could this question some how be referring to the Elder Scrolls lore that vampires are considered undead? Maybe the key to entering is to be undead?)
I am only suggesting that maybe the Volkihar will be a new evil faction that is joinable in the game. I am in no way trying to say that the Dark Brotherhood are out of the game (as they have already been confirmed anyways), and just that maybe their lair is located somewhere else.
Links to where I gathered my info:
http://elderscrolls.wikia.com/wiki/Volkihar_Clan
http://elderscrolls.wikia.com/wiki/Vampire
http://xbox360.ign.com/articles/118/1186214p1.html
What are your guy's thoughts on this? Maybe I am being a little too eager, and just looking too deep into things.