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.
Cryptocurrency will be used where it is convenient to do.
The better and more convenient the infrastructure for using cryptocurrency in the country, the higher the likelihood that each individual citizen will use it.
In developed countries, everything looks much better than in less developed countries.