While not something I'm really pitching and probably won't ever do, something I'm curious of would be a minecraft-based RP. 

I'd assume it'd be like a survival RP but with more blocks and perhaps inventory counting management.

It would come with the added bonus of players being able to directly show what their character would be doing through in game screen shots which is an interesting idea in of itself but I'm not sure how many other situations this can be applied too.