together with the development of currency, i think fiat currencies will not necessary anymore. Cryptocurrencies have so many advantages over fiat. It will soon be replaced by cryptocurrency.
This will happen but hot that fast. Reason for this are many and those reasons are mainly in global level. If something has to change then ok but still more then 80% of world countries are still really on fiat or gold. Crypto is even ban in many countries so doing this will require lot of first time then effort to adopt everything in regular day system. Why cuz we pay fee for every transaction no matter how small that is and this may be problem for many countries that are even considering this option and implementing crypto payment in everyday. Maybe after few years and when we see how Japan model when with some information about we will be able to say little more specific and detailed.