I'd like to see Damian Priest be world champion, guy definitely has what it takes to become one, I love the sound of a feud between him and Roman honestly, and Roman putting Priest over would create a new star for WWE. Have him win the Rumble
Riddle also would be interesting but I think the feud with Randy is what he'll have for WM, but I think he'll be in the main event scene by next year.
For a while I would have said Drew, but man the guy has gotten really stale as a face lately, he's just not that interesting anymore IMO, I really think Roman should put over someone new instead of a made man like Drew.