Could the debate over Cumberbatch not resembling Montalban be summed up by the fact that future Khan was killed in the Genesis Wave and was regenerated in favor of a new matrix?
So, the Genesis device was programed to destroy everyone and remake them blue eyed and white? Wait until Hitler (or the GOP) gets wind of this.
On a different note, why would the explosion of the Genesis device in the future have any impact on Khan in the past? Such a plot twist would serve only to completely confuse the audience (I'm even confused trying to figure it out).