I think that they will never accept the cryptocurrency as a whole.
Considering that every country has its own laws and economy, is it possible? So, will the whole world change to accept a single cryptocurrency? No. Like it is hard to create a new one. lol
I think it's possible because they have unlimited sources and they can create new crypto for their country. But they need to follow the rule in the cryptocurrency and each country cannot easily to add their crypto to the crypto list. But I don't think that every country could do that because there still many countries can't create new crypto and they could only use the existing crypto which is bitcoin or another coin.