Could you see a future wherein the entire world shares one global currency, be it fiat or crypto? If I think it in a scifi kind of way, it would most probably be some digital currency that could all just use. It doesn't even have to be in this century. Maybe the next?
Dollar is our national currency and i think it is not difficult to have a global currency if every country will have a one concerted either fiat or digital currency to become a global currency.