I often wonder, had they cast Benicio Del Toro as Cumberbatch's character, as it would seem Del Toro was an early choice; and now we would be seeing Del Toro doing all the things and saying all the lines we've been privy to in the trailers, AND THEN, we were told that it's not Kahn, but a guy named John Harrison, it would be easy to say: "Fuck that, he's Kahn, no doubt about it"....
I think it's all a red herring, I would even go so far as to speculate that even the early casting consideration of Del Toro was itself part of the misdirection... perhaps he was never in the running, but leaking the news of his possible casting (and other actors of latin descent) would had all the buzz on Kahn before the movie is even made, making any actual "non-Kahn" plot that bigger of a twist and surprise.
I think this film is more about nationalism, terrorism, capitalism, a post-Vulcan weakened Federation, conspiracy, an anti-Starfleet movement, and Klingons. I believe the Klingons are playing a much bigger role in this plot. While Kahn can easily be a villain to facilitate all those themes, in my mind, it's mostly subterfuge.
---And if Del Toro was in the running, he could easily pass as a believable "ridgless" Klingon of the TOS era, perhaps the true Harrison is an altered Klingon sleeper agent. (crazy right?) Merely playful speculation on my part.---