I'd strongly recommend dropping the morally gray/evil characters only angle. Villain-only games have been attempted in the past, and they've all run up against the issue that it just isn't very fun to play a villain without any non-NPC good guys around. A pivot to focusing on evil characters + the corruption/downfall of non-evil characters might work out better.

Otherwise I like the proposal a lot! Ravenloft is such a cool setting and I think it'll do well as a DWRP game.