I think the future of cryptocurrency is going to replace cash. Because now some countries are planning to cancel the cash and only use the cryptocurrency.
Your opinion is partly correct, because cryptocurrency will become digital money in the future. But for cash transactions, still use paper money. So as a means of payment in the future, cryptocurrency will coexist with paper money. So that people are free to choose which one is preferred.
Not possible the least for any country with normal economy to cancel its fiat and launch crypto instead. It would require huge reforms and shift in structures that no country will deliberately accept.