I would love to see a minor RE character come back, as I think Leon/Claire/Jill/Chris have been way overused and if Chris gets any bulkier he'll implode!
My ideal character to come back would be Barry, in a sort of MGS 4 Old Snake kinda way. We haven't heard from him since 1998 and it would be interesting to give the playable character some vulnerability (in this case, his age) to make the game scarier rather than beefing them up all the time like Chris in RE5. I would also settle for Carlos Oliveira, Billy Coen, one of the Outbreak characters, even Ark from Survivor. Just. Not. SHEVA.