Vayne + Sated Devourer = HO. LEE. SHIAT!!!!!
Yeah, I think it's safe to say that a Vayne with Sated Devourer would be broken. But considering how hard it would be for Vayne to get there in the first place... Riot's probable word on it would be "If you let Vayne get there in the first place, you deserve to lose."
I doubt we'll see it much, but on the times we do see it, people are going to bitch.
36%max hp every aa