Wouldn't be better to call "champion" monsters "nightmare" monsters, since that's what the uprated imp was called in Doom 64 and what the uprated caco and spectre were called in Doom 64 TC (which admittedly was a mod rather than an official game)?
Anyway, as long as Kornel's thinking about formers for a new DoomRL, here is another rough concept that I think would help to "fill out" the various types of people one might have expected to find on Phobos base before it was attacked...
Former medic:
"The bad new is this guy hasn't lost his extensive knowledge of medicine, meaning he can heal and, with some effort, even revive his fallen comrades. The good news is... well... other than that he's no tougher than any other former, there is no good news..."
Essentially, the former medic would be a lesser arch-vile and would either have the ability to heal nearby zombies and other bad guys, revive them from the dead if he is standing on an adjacant tile (meaning he can raise the dead, but not as effectively as a vile can), or both...