Criminals would be stupid if they use semi-anonymous cryptocurrencies. If cryptcurrencies are to be used, it should be fully private dark coin coins. I am not sure whether this is currently the case (security and privacy are still to be rigorously tested).
As 'money changers' are concerned, regulators will try to enforce existing laws, whether successful in the end or not.
It will only become a blockade if regular exchanges are prohibited from taking fiat in exchange for crypto. I do not expect that to happen soon in the EU. It will probably be just KYC checks. Such checks are not that prohibitive (many exchanges already ask for KYC docs, especially if amounts to withdraw exceed certain thresholds).
Criminals will avoid exchanges anyway, again because of the privacy aspects.
All in all, I see good days ahead for dark coins.