At least do something we haven't seen much of like the Gorn. Please no more Borg or Ferengi. And if they HAVE to rehash a Star Trek story, do something different. Khan wasn't the only good story told in the original Star Trek.
No, but outside of Klingons and Borg Khan is the most well known character, and he is one that hadn't already been done to death in other incarnations.
Everyone knows when you get a box full of toys you've never played with before you always play with the best ones right away, with the exception of Batman Begins but I think that has more to do with Nolan thinking every Batman villain was silly and wanted something that felt more "real".