My first guess is Wally. Before Savitar grabbed Wally I was commenting about how it all sounds like things happening to Wally, then Wally gets trapped in the speed force and I'm like: Yep -- he goes insane, blames barry for not saving him, and becomes Savitar.
That could just be a red herring though, so my second guess is Eddie Thawn. No specific in series hints, just seems like something they'd do and I'm thinking I'd read that the actor was supposed to appear on the show again.
e-