Good historical perspective and timeline with a number of considerations set.

I am informed vast amounts of US dollar bills circulate and never return to the USofA. Also informed, living in East Africa and still a strong cash economy despite major shifts to digital engagement, vast amounts of what counterfeit to the USA but act as trading paper in a number of settings.

Different levels for USDollar operations.

Will the digital shift cause further capability to change denomination and thus ease of trading to whatever means of exchange is required? Will we witness more barter - raw materials out traded directly against finished goods in with different forms of delineating rates of exchange/trade?

Who needs currency?