If they do release an expansion, there are a few "Races" I can see being used.
Ogres, maybe giving them something that removes corruption for dial counters *They eat, and eat, and eat, and... wait, where's all the food?* and they do worship the Great Maw.
Vampire Counts, because most fiction of them tends to involve the mass corruption of the surrounding landscape wherever they set up shop.
Granted, I think the biggest flaw with the expansions is that most of it's a case of "Been there, done that" with the four gods. It's a bit hard to think of something unique that doesn't tread on any god's style.