One other thing. Blood has to be matched for type (except for Type O). While it would be logical if Khan's magic blood "fit" everyone like Type O does, maybe it doesn't. It could be a happy coincidence that Khan and certain others have the same blood type. Maybe Marla (in the Prime Universe) didn't share Khan's blood type.
What if it changes those who receive it? Be interesting if it had nanites which began augmenting the recipient. That or specialized viruses.