We all know that BB has never been 'mainstream' in the same way as biggers sports such as MMA, or even Miss USA contests for example.
Despite this i'm pretty sure that the top dogs in the IFBB would love for this to happen, and they probably try to get a little closer every year.
Having a freak like Kai Greene as the face of proffessional bodybuilding, even if he's only Mr O for one year, would severly hinder any efforts to push BB forward to a wider audience.
So even if Kai 'wins' an olympia hands down, he will never be given the crown for that reason alone.
It would be like trying to get your locally produced protein bar business out into the wider market by using the face of some random criminal bodybuilder wierdo in your gym.