My possibility ratings:
Colonel Green or associates: 20%
Well, I suppose it's better to be 5% correct than 100% wrong.
Im not saying it can't be Khan, only that so far, the details we know make it sound more like Gary Mitchell. If it IS Khan then there are significant changes to the original timeline and character. I don't like Khan being in it, but if it IS him, I will reserve judgement till I see more footage.