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?
Crypto doesn't have any chance to become global currency in this century since the people's ties with traditional fiat money are too close. All banking systems with millions of their transactions are bound to fiats, these systems have become convenient and familiar to so many customers that I wonder what could make them shift to crypto? Anyway, if this happens it will take many decades - I don't think I will witness the victory march of cryptocurrencies during my lifetime.