The same sorts of computerized financials that make possible the recent rapid growth in Electronically Traded Funds (EFT's) that enable me to conveniently trade, long or short, all manner of specialized markets, currencies, commodities and precious metals is also enabling the big money players to trade and hedge between multiple currencies in a highly liquid market.
Currencies will become just like another commodity; I'll use copper to wire my house, copper or PVC for the pipes, and dollars to pay my butcher. Those in London will use pound sterling to pay the butcher, rather than dollars, but otherwise trade in the same world wide markets as do I for any significant transaction.
I anticipate that baskets of currencies, perhaps viewed as S&P 500 indexed mutual funds have been viewed by investors for the last 50 years, will become the new currency for any significant amount of money. Whereas the mutual funds traded once per day, with limits on trading frequency to perhaps once or twice per quarter, these baskets of currency will trade in real time, around the clock.
Having the dollar as the world’s reserve currency is what lets the USA get away with printing money with impunity without ending in a Weimar situation. What happens in your future world when the US wants to print money out of thin air?