IMO simpler is better. A legal guarantee for anonymity that might end up being backed by complex technology is worse than a legal guarantee that you can pay with paper money regardless of anonymity. That's because paper is less likely to have an unnoticed back door (what anonymity does Bitcoin provide if your PC is running a keylogger?)

In fact this makes me think of all the nice things we could have if support for simple mechanisms was legally required in various areas of life.