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?
The kind of world using one currency is not feasible now or in the future. The whole world is not at the same level of development, either in terms of infrastructure, economy or political stability. This kind of wide imbalance between countries will be an hindrance in achieving a one world currency system. But like you said maybe the next century, who knows?