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.
No, it will not going to happen, in the first place, cryptocurrencies are decentralized, it has no third-party that can interfere with its transactions such as banks, financial institution, tax related organization and almost anyting. Unlike the fiat, there is something that has an access in order to take a control of it.