You know, those races are very good but... I think we should follow the trend with Fyreslayers and Kharadron Overlords. Select a thing in the Warhammer Fantasy universe and up it to 11.
My pick? Vampire Blood Knights.
A faction of Blood Knights, fusioned with Wizards that use the blood of his enemyes to fight. What kind of big model they can have? Abhorash! Abhorash in the form of a Big Dragon-Knight (Literally, a bypedal dragon-knight ) hybrid with lots and lots of blood.
The concept in my mind was something with a resemblance to this:
Vampire Knights mountind mini-blooddragons, Knights on foot (Vampires too, obviously), even Abominations made of pure blood.
The Fluff can't be easier. A rivalry with Khorne, you know, he has the monopoly of blood for too long.
Death its the Alliance that need more variation in its themes. And need it fast!