I don't think that cryptocurrencies in the next couple of years will be able to become so strong that we forget about fiat. And if it happens that states adopt a digital currency then it will definitely not be bitcoin, in El Salvador this is an experiment and that is an addition to dollar.
Crypto currency is getting stronger, bigger and wider more than expected and triple the people's global awareness about crypto. How's that possible? Basically the NFT and gaming industry has a lot of contribution to open up the mind of the people that crypto is not all about ponzi and scam as what the people normally think.
The proof is already prepared and now is so evident and couldn't neglect the fact that cryptocurrency is becoming strong.
Well, with regards to forgetting fiat. I don't think it as easy task since the world is so much fan of fiat. That is why as you can see the wide range use case of digital transaction not limited to cryptos. Money, ticket payment, bill payment, rent payment, insurance, education, negotiations, and etc.., are the door to easily embrace how crypto works.
The world are getting close to crypto use case though it might take some time yet the effect is slowly but surely. Big impact cannot be denied.
In the future fiat is possible be intangible value (who knows).