Srar, Gary Mitchell appeared in the episode "Where No Man Has Gone Before", the second episode produced and the first to have William Shatner. Originally a friend of Kirk's (and helmsman, he, along with Elizabeth Dehner, gained god-like powers until Kirk managed to best (and kill) him. Dehner was a bit more gracious.
But yeah, I guess it would make sense, so long as it's not a new character
Why I believe it's Mitchell (pictures in the spoiler tag as a size courtesy)
That and BC's character wears a uniform; this would seem to indicate Mitchell, but Khan also wore one in "Space Seed".
I don't think it's a new character as I've heard it's definitely a character from previous Star Trek canon. Gary Mitchell makes the most sense with the casting of Alice Eve who could be Dr. Elizabeth Dehner. Then again she could also be Lt. Marla McGivers from Space Seed but she definitely resembles Dehner.
However, Gary Mitchell didn't posses superhuman strength or agility but Khan did. Since this is an alternate time-line though I think it's Gary Mitchell.
As long as he's better than Eric Bana's character Captain Nero, I don't care who he is.
I liked Nero
He was the worst part of the first movie. I also didn't like how Kirk was used as comic relief when he's supposed to be the main character. Also, Scotty's little alien sidekick just reeks Star Wars rip-off.