I found this expression on the news channel about the crypto currency: "Anyone who will try to buy coffee for cash in 2023, runs the risk of causing laughter from the seller, that he does not use crypto currency."
how do you think, is it realistic? Can a crypto currency replace national money?
I think that it's possible, but it will take more time.
Yes it is possible, remember some countries now have their own coins. Countries can create their own coins and declare it as their national currency. They can make it decentralized and also make their coin backuped by their FIAT.
I think it is impossible to replace national currency with crypto currency, what you presented most probably to add alternative tools from their national currency to be exist in crypto space. Perhaps it is similar to USDT which represent USD in crypto space, the value is almost same just different in crypto space as virtual type and national currency as actual type.