Just a theory about the plotline for Skyrim's newest piece of DLC. Based off of the trailer and the many interviews during E3, I blieve that the plot will go something like this;
The Vampire lord wants to block out the sun. This much I believe is odvious. In order to do soo, he will need to sacrifice his own daughter (as stated in the interviews). This puts him at ends with his wife who, dispite potentially condeming all vampires, will not allow her daughter to be sacrificed. During the main questline, I believe that you will have the option of either helping the father or the mother in their goals (or even the daughter). If you help the father, you are rewarded with a number of vampire related goodies and some new title. The main plus would be that you can now go into the daylight as a vampire without taking any sun damage or suffering any penalties. If you help the mother, she dies near the end (after defeating the father). This leaves you in a position to marry the daughter and become the new vampire lord. The sun is still a treat, but now you get a number of bonuses and a few powerful followers.
Just a theory on how the plot may unfold. Comments?