Ah right I see the problem here, I doubt fel and light blessed worgen would woork out well....or it could create and interesting situation where the champion starts losing his mind as he starts wielding fel power and has to seek out a replacement for the light. Hell maybe the Legion promises it to him in return for his continued service.

I'll back off for now and let other people develop their factions though, but if someone decides to play the Legion I think I could potentially make it work, assuming we assume the Light works in that way as opposed to the character instantly going back to his feral state the moment he uses fel.