The massive government intervention will be, they will simply prohibit US business from accepting bitcoins. The Treasury has already said they do not recognize the currency as its not backed by a foreign government. This commenter in a recent article said it best:

Bitcoin has one major flaw. In order for money to be valuable, one must be able to exchange it for goods and services. If the US government perceives bitcoin as a threat to the USD, the US government will make it illegal for businesses to accept bitcoin as payment. That will make bitcoin virtually worthless - at least to Americans and anyone doing business in or with America. The government cannot do much about bitcoin itself but they can prevent businesses from accepting it as payment.

Bottom line is you have a glorified penny stock scheme. And like all penny stock schemes, when people start selling only a very few make any money, few break even, some lose money and the rest lose all their money.