All governments and countries in the world are depending on fiat, every economy is based on fiat and cryptocurrencies can't change that. And besides because of crypto nature they are not convenient to build economy on their own.
But with regulations and adoption government can support cryptocurrencies in.a way or to be more precise on that way Bitcoin and other coins could be introduced in traditional economy system and help them to become more equal and accepted.
It is not convenient to build your own economy.
Other currencies may be introduced in the traditional economic system and make them more equal and more acceptable.
Government can (support) electronic money but not replace current currency.