Maybe the question is what would happen if bi becomes the official currency in one of the countries in the world, although this is not very likely because of changing the whole economy system.
But with lehgal regulation we would do no harm to Bitcoin, just split legal of illegal use of it so that could help us all.
I wouldn't say that bitcoin is not regulated because in many countries is not considered as currency but as agreement that is as form of payment between two parties. For this reason there is no regulation. Furthermore, there will not ever be any government to adapt bitcoin as official currency of his country because is not centralized. That means she cannot have the control on their citizen's wealth.