Been reading over this thread and have to admit, looks awesome.
I've played Lithians' Nature Of The Beast and Terran Vampires (which was great but I didn't find too RP or Lore friendly)
Anyway, want to add just in case no one stated or anything but if the storyline involved obtaining Molag Bal's blood, it could be done through obtaining his artifact.
I think that the "Blood Of The Daedra" quest might have been forgotten...
Perhaps make a new Molag Bal artifact and have a struggle between the factions to have possession or control of it. I won't go into effects or anything.
PS. Sorry if too late. I was reading past posts and practically screaming at my computer to let me put this there. Oh and if I missed something lorewise or threadwise, my apologies.
EDIT: Wait, seems like it is way too late. Oh well, seems like a nice add-on or end-quest.