Originally Posted by Menel'dirion

I like this idea. It's a fresh way of getting new classes in. Might I suggest another:

The Dreadlord: Yeah, it's a Demon, not a class, but hear me out. Requirements: sufficient leveling as both a Warlock and a Priest.
Lore Functionality: You are a Demon, but you are possessing a humanoid host (just like Westwind and Dathrohan) (which is the race your choosing). Perhaps you'd start as a human cultist, and then you screw up and summon a Nathrezim to possess you.