for now I think can not replace the fiat money because some bitcoin countries are still not in the official, maybe if later the government has inaugurated bitcoin for that bitcoin can replace the fiat money ...
I guess cryptocurrencies for now is hard to say that it would replace the fiat existence in our society because crypto is not yet accepted legally in some countries and my country is belong to those countries who are not yet accepted it. So it is hard to utter like that today with regarding to the subject but of course we always hoping for a positive results of crypto's.