Hollywood Reporter say:
Alice Eve is in negotiations for a significant role in Paramount's second installment of the J.J. Abrams-shepherded Star Trek reboot. [...] Little is known about the Eve's character beyond that the role is significant.
ETA: I derped. Apparently Eve's charactger is going to be someone brand new. Plus there's this interesting tidbit:
Del Toro's role is likely a familiar Trek character and that he'll be accompanied by another, older supporting villain that has yet to be cast.
Pretty much rules out him being Khan, I think, which makes me happy. Can't really think of who ELSE he might be, though... Maybe some Klingon dudes, is my best guess.