You can do Klingons or Romulans in a interesting different way because that's a species of characters we're talking about. Khan is one character. Known for one sequel iconic in both its popularity/success as well as parody. Big difference.
I'm not a writer but I think it would be easier to do one character in an interesting way than a whole group (plus don't forget that Khan also has approximately 80 genetically-engineered supermen. I think that opens up a number of possibilities.) Also regardless of how iconic Khan is or was, that was over 30 years ago.
Are you telling me that Khan is more iconic than Kirk and Spock? I cannot think of any characters in pop culture with more popularity/success and parody than them. By your logic, JJ's Star Trek shouldn't have been a success (many people for sure was certain it would fail) and I've heard some of this same logic applied to Nolan's version of the Joker as well. Nolan offered his interpretation of the character and I would be interested in JJ's interpretation of Khan (but only if he is inspired by the character. If he has no real interest then I pray that it would not be a studio mandated decision.)
Its time to step up the the challenge rather than hiding from it and making the excuse that's its lazy to do so. Its actually lazy not to. Whether they introduce him now or in the next sequel, Khan is a great character from Star Trek mythology and not to use him again is a crime. ,
And again...they're welcoming the comparison. Worst of all they already did the Khan story. In the reboot. With Nero.
Yes, they did the Khan story from ST2 but it have to be that story in any new movies.
Don't see how anyone doesn't see this as lazy given how much they made an effort to reboot in a fashion to please the hard-core fans and get in the general public. It doesn't "need" Khan at this juncture because the reboot was so overwhelmingly received. General public wasn't walking out during that summer clamoring for him as the villain, just fanboys with zero imagination.