The assumption would be that if the villain had remained Harrison, there wouldn't have been people in the tubes (and maybe no tubes at all). Harrison's motivation would have been completely different.
And that's my point. It would have been a completely different movie because Khan and the Eugenics element would have been gone, including Admiral Marcus's motivations and the existence of the Vengeance. But those things were staples right from the start of production. I'm just not buying that the villain was ever going to be anyone else but Khan, even with what Wormhole is claiming. Orci may have been the one to insist on Khan, but I doubt that was a very long meeting:
Kurtzman (right after debut of Star Trek '09): "So who's going to be the villain in the next movie, as if we didn't already know?"
Orci: "Well, we're in negotiations with Benicio Del Toro, so we're all set to start writing the Khan story."
Kurtzman (chuckling to himself): "But are you sure we shouldn't have another villain, since
everyone's going to think Khan will be the next villain? Somebody like, maybe that dude that was in the pilot episode with the glowy eyes?"
Orci: "Larry Mitchum? Nobody's going to care about that guy or even remember who he is. We gotta do Khan."
Kurtzman: "But, what about that other dude, the fat guy with the mustache with the annoying wife and prostitution ring?"
Orci: "Well, then we'd have to make Del Toro bulk up and make him grow a silly-looking 'stache. We don't have time for that!"
Kurtzman: "Okay, okay, quit the browbeating, we'll do Khan!"