In the future, there may be exchange standards for multiple currencies, some relying on gold and silver, and some relying on Bitcoin. If another superpower emerges in the future, it is also possible to formulate a fairer world currency and a new economic system.
The new world order that is already established has split the world into regions where super powers dominate there and they can form alliances and relations between each other. There won't be any unipolar world any time soon. In these regions there will be certain currencies in use which could be converted between powers but again there won't be a singular currency to be used globally. It would take time for this new order to solidify though.