My only problem with Khan is that most people automatically associate him with The Wrath of Khan, which even if this movie were to be a re-hash, it wouldn't be of TWOK, it would be of "Space Seed". And considering we've got Peter Wellers on board as a supposed "secondary" villain of sorts, that doesn't fit with "Space Seed".
Honestly, they could just give us the title and I'd be happy. Calling it Star Trek XII is only marginally better than "Untitled Star Trek Sequel".