Sure “John Harrison” could really be Khan or Garth of Izar or some other Star Trek villain, but based on Abrams Trek I, he’ll be a character so undeveloped and with a backstory so weak that if you poured hot water over him you wouldn’t even get tea.
Star Trek Into Darkness is written by the dream team of Roberto Orci, Alex Kurtzman and Damon Lindelof, better known as the writers of Transformers and the guy responsible for messing up Lost and Prometheus. It stars a lot of special effects and probably not much else.
Maybe I’m wrong. Maybe John Harrison will be more than another villain with no credible motivation looking to wreak havoc for the same non-reason that most Bond villains do. But I wouldn’t bet the space farm on it.
Nero in Abrams Trek I had a big name actor, a suggestive name and a backstory that made less than no sense at all. Nero had less credible motivation for his killing spree than every other Star Trek movie villain, a list that includes a guy who was obsessed with plastic surgery and another guy who ran his own cult. (These stories come out of Hollywood so they’re true to life.)
Nero lost his wife and his homeworld because Spock didn’t get there in time, so he traveled through time to destroy Earth and Vulcan. Six year olds could come up with a more coherent motive for a villain than that.
In a measure of Into Darkness’ bold originality, Harrison will blow up London and probably San Francisco, because Star Trek is now completely indistinguishable from Transformers and even has the same writers.