As it stands, it barely has any relevance to the story that Harrison turns out to be Khan and he could have easily been replaced with an original character to much better effect.
I've seen several people make this comment. It would probably have been better if Harrison was not Khan, but an augment created by section 31. Possibly based off Marcus' DNA. That could also excuse the "magic" blood. The blood may not need to be "magic". It could have modified Borg nanites retrieved from wreckage from the Narada. The comics before ST:09 did say he had Borg tech, right. And we've seen them bring seemingly dead drones back to life.