I’ll look into MMT. As for cryptocurrency, it’s hard to see it replacing a currency such the USD or EURO before the equivalent is issued by governments, but it seems very possible to “sneak up” on smaller countries and be the “commodity” of choice for many transactions. Much of the economy is already unreported transactions in countries, but they still use the fiat currency. If cryptocurrency is as convenient as and widely accepted as fiat currency, I wouldn't classify it as a bartering system rather an alternative currency.