Whoever it will be, I doubt that we get more than one character. Ed Boon told that they outlined their whole summer reveal plans before E3 and he never even mentioned EVO back then. So MKX will be at Comic Con, Gamescom and PAX for sure and NRS have their plans for those events, EVO is some kind of bonus for hardcore fans.
Raiden would be too obvious at this point, but based on the Injustice coverage we may get three demo matches with the three versions of the revealed kombatant and that will be it.