See the case of E-Gold for a similar comparison. E-Gold was doing something very similar: letting people transfer money anonymously and untraceably, but backing it with real gold in a vault so that it had some legitimate worth. The feds shut them down.
Crypto currency sounds great, but unfortunately it always breaks down where the rubber meets the road, or where the crypto currency gets converted into real currency. These places are easy to shut down by any government.