I still don't see how the value of that "unit of account" will be determined. Something costing "two bitcoin" is meaningless if people do not have a reference point up against which they can determine what it's actually worth. It's like good and evil, you can't define one without the existence of the other.

On my second question: Imagine having bought Bitcoin at two grand a piece, The fiat system collapses, a new one comes up with a new global reserve currency (which could be the SDR) and a sandwich ends up costing the equivalent of 8 Bitcoin.