If you would want to know that exactly, then... no one will give you the right answer. We may give our assumptions but those would be considered as an opinion and not a fact.  It may replace fiat in the future since a lot (but not most) people are looking forward for it to happen. But that would take a long time to happen (talking about the arguments with the government and central banks of each country). You see, most people nowadays are not that familiar or interested with cryptocurrencies (some) they may know what it is but they are not using it or probably they are not that open to the idea of replacing fiat money.