When economists say something won't work because of [... whatever] they are saying they would advise against it, and those in control of the monetary systems heed that advice.
But today, I am my own bank. I do maintain some control over the "monetary system" (at least, the parts I interface with).
If I have bitcoin as MY reserve currency, then there is no THE reserve currency, there are instead reserve currencies. As in multiple.
Efficient or not, .... Harmful to economic growth or not, etc etc ... that can (and likely will) be our future.