Oh man. I think we have it. Maybe we're reading too much into it, maybe it's a lot of speculation.
In the Art of War I definitely see the Predator's final attack to the cultists around the artifact. Definitely looked like a corruption / fire arrow to me.
My brain went wild with this concept. I really hope Rogue gains access to modify other classes to harness corruption and not just darkness.
It brings an interesting concept to the idea of a 'Dark Knight' style class. Rather than using some dark void essence or undeath to harness.. Well, fiery emotions - Fury, Anger, Rage .. Maybe Revenge, Spite... Stuff like that.
An interesting concept.