Agree. Not all nations have the technology to implement the cryptocurrency system in their economy. So I think that the currency of any nation will remain in its finances. If there will be the handling of cryptocurrencies in cities that have better technology infrastructure.
I have seen it in my country. When the banking system implemented mobile payment and not all citizens have access to a smartphone.
This problem may also be encountered by those who have a Bank card at a time when there is no electricity and there is no possibility to use the terminal. Therefore, in addition to a credit card, everyone should have a Fiat. And you correctly said that in order to make a payment in cryptocurrency, it is necessary that everyone has a smartphone to make the payment.