There are a variety of different regulations that could put on cryptos, without outright banning them. However, make no mistake, any significant regulation will undermine the currency as a whole. The first regulation, that I believe will happen quite soon in the United States and Western Europe, will be a requirement to register your wallet. For most owners, this is easily accomplished by their hosting service, such as Coinbase. By doing so, some level of anonymity no longer exists. Yes, individuals could disobey this order. However, unfortunately, most would obey the law. This would make transfers between registered and unregistered wallets, quite risky for the "legal" individual.
The next level of regulation, which is largely impossible without anonymity removed, is taxation. As far as I know, profits on cryptos are only taxable if the individual takes them out of cryptos altogether. I suspect that this will change. If you profited in a new altcoin, and you want to park your profits in Bitcoin, I believe the government will begin treating that as a taxable investment profit. I'm not convinced the government is all that interested in this small chunk of revenue; I think they would institute such regulations in an attempt to squash high amounts of fiat being traded in for cryptocurrencies. To that end, I think it is possible that countries such as China, would limit the amount an individual could transfer into cryptocurrencies, in a certain time frame.