Why did he specifically have to be Khan, though? Would the film have really been missing anything if he wasn't?
FACT: If the writers had made this an original
villain, a very large group of Trekkers would now be screaming:
"Missed opportunity! Imagine if this had have been Khan instead! We could have seen how this timeline's Kirk and Spock would have handled him!!!!! Orci & Kurtzman - the coward fools! - weren't brave enough to tackle Star Trek's finest, most well-known villain. He is the equivalent to Joker in the Batman comics and movies!"