In a way, Khan was
the back door. While Damon Lindelof wanted Khan to be the villain from the start, Roberto Orci didn't want to use him, and insisted that they develop the story with an original character as the villain, in order to ensure it could work as a standalone story rather than just continuity porn; and then, once they were confident in the story they had, they addressed whether it would still work if the villain were Khan, and they ultimately decided it would.
But the idea that they only used his first name because they thought they might reveal he was, say, Khan Jones instead of Khan Singh? That's just bizarre. The name "Khan" carries a clear and unambiguous meaning to Trek fans. They wouldn't call a character Khan unless it were meant to be that
Khan. (Genghis Khan from "The Savage Curtain" and Zor Khan from "All Our Yesterdays" notwithstanding, since neither of them had any prospect of showing up in a 23rd-century story.)