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.
Recently, the Chinese government made it mandatory for the merchants to accept payments in physical cash, after promoting digital payments for more than a decade. A lot of the citizens (especially the elderly), still find it very challenging to use the online payment methods. And not all of them own smartphones. But for cryptocurrency users, we can get around this problem by making physical Bitcoins. Anyone remember the Casascius physical bitcoins?