Cryptocurrency is the future of all payment method due to the decentralized nature which grants financial freedom and power to the people. However, for it to replace cash or the Fiat, it will take years of awareness creation. Up to date, some people do not have access to internet whereas others do not know how to access it.
Cryptocurrency can never replace the national money of states. It is designed to create an alternative payment system, and not to replace the existing payment system. Due to many reasons, including high volatility, decentralized cryptocurrency will never replace fiat. Here our desire is small. Cryptocurrency can not support the development of the economy of a particular state, because it has nothing to do with it. Therefore, governments will never decide on such a replacement.