Not sure how they would do it but I expect every time before you make a withdrawal, you will need to submit a long list of supporting documents that require yourself to declare some statements concerning where the coins are obtained. Also they could make it mandatory for companies dealing in bitcoin to register and comply to certain guidelines. I see good and bad to it.
I'm sure there will be both positives and negatives to regulation, but one thing is for sure there's nothing we can really do about it. Regulation is inevitable but were going to have to play by their rules whether we like it or not. I can opnly hope that they're fair and don't actually cause harm to the bitcoin ecosystem.