That's interesting, because I don't think anyone can be the frontrunner for a role that currently does not exist. "We're not even at that stage yet," Abrams told SciFiWire. "But the fun of where we are on the sequel is we could use some of what was done before in a new way. But we haven't even figured out what we would use yet, so it's very early on." While Abrams and company haven't ruled out the use of Khan, they also haven't tied down the specifics of a story, which would make any casting talk no more substantial than fanboy spitballing.
It's easy to connect the dots between actor Carbonell and the rumored role. Carbonell definitely looks the part, and Lost is also an Abrams production, so it makes sense, but until Bad Robot actually confirms anything, I'd take all Star Trek II rumors with a big grain of salt.