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?
There is no probability that there would be a global currency. Every country has their own unique pride and has individual gold deposit in the world bank. The wealth of a country depends on how strong their economy is and that's the reason why those rich nation will not allow to have a global currency. It would be unfair for them to have the same currency to those poor country and trading would not be advantageous for those rich nation is global currency exist.