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.
Thats only if you do it throught a bank. They can't stop P2P (as in person to person) direct local exchange of BTC for cash. There's always a risk of it being a trap, but if you buy from a trusted seller form LocalBitcoins nothing wrong should happen. It sucks tho, it makes adquiring Bitcoin as if you are adquiring god damn coke or something.