The need for fiat currency is currently maintained in many countries but I think it will gradually be abandoned. I was quite observing in terms of raw materials and real ownership of money between the fiat and crypto currencies.
1. Fiat currency requires special raw materials and this will continue to grow and will eventually run out, if so what happens is the sustainability of fiat currency? Crypto does not need this raw material because they are non-physical and no longer cost to procure raw materials.
2. Can the country detect how much money is actually in each person if they don't report it? Crypto already has a decentralized ledger and this will be very useful for tax imposition, transaction flow and prevention of money laundering and criminality