Major Spoiler Alert: Speculation that Khan Noonien Singh would once again menace the forces of Starfleet in the as-yet-unnamed Star Trek sequel appears to be unfounded. Actor Karl Urban, who has reprised his role as Dr. Leonard "Bones" McCoy in the sequel, accidentally let slip what director J.J. Abrams has kept under wraps, the identity of the villain in the film.
When, during an interview with SFX about his lead role in the new Judge Dredd film, Urban was asked about working with Benedict Cumberbatch on the Star Trek sequel, the actor replied: "He’s awesome, he’s a great addition, and I think his Gary Mitchell is going to be exemplary."
Gary Mitchell, as fans of the original series know, was a Star Fleet Academy friend of Kirk’s, who as the result of an encounter with a "galactic barrier," acquired extraordinary telepathic and telekinetic powers along with a serious case of megalomania.  Gary Lockwood played Gary Mitchell in the classic "Where No Man Has Gone Before" episode, which was the second pilot episode ordered by NBC (at the behest of Lucille Ball).  This was the episode that got the series on the air and established the makeup of the original series crew.  It marked the first Star Trek appearances of William Shatner (Kirk), James Doohan (Scottie), and George Takei (Sulu).
Cumberbatch, who is brilliant as the nearly superhuman sleuth in the BBC’s Sherlock, would appear to be an excellent choice to play Mitchell, who doesn’t shy away from referring to himself as "godlike."