I was going to say 'could make a WoW sourcebook' but ... There's actually already a WoW RPG from White Wolf games, and apparently a Monster Guide that "Includes full rules on monster abilities, on improving monsters, and on using monsters as heroes, villains and player characters."

Yeah, I know, you mean in-game. it'd be nice, but apparently they think it would be too good without nerfing. ^.^