The government can't stop crypto currencies any more than they can stop drug trafficking. The only real threats to these currencies are people not valuing them or the development of quantum computing. Quantum computing will be a reality before people give in on cryptocurrencies
I don't think the war on drugs was designed to stop drug trafficking, but to feed the prison system. Not only that, the State has become the premier dope dillah : weed, booze, prozacs, percs, oxys, adderall, viagras, they got it all yo. Their approach is Demonize, Criminalize, then Monopolize.
I unfortunately think they could pull off something similar with these currencies. Either that, or they'll manipulate public opinion enough so that they'll go way under the radar. Just look at 3D printing. Why isn't there one in every single home?? It's too disruptive.
One can hope, yeah. History almost teaches us not to.