I mean it's not impossible, and I think that with technology evolving at a fast pace so does cryptocurrency and the whole market, blockchain will definitely become much stronger and secure in the next decade or so, and it is possible that crypto will be able to replace fiat if the government finds out the advantages of crypto and how it could benefit the economy.
Cryptocurrency can never replace the usual currency of the state. I think that in general no state will ever give up their national money in favor of cryptocurrency. While on our planet there will be many different states with conflicting interests, they will always use their national money. This is the key to the success of their economic development. It is very dangerous for the economy of any state to switch to the use of a foreign currency or "neutral cryptocurrency". Therefore, there is talk of replacing national money with a cryptocurrency, nothing more than an imagination of people who have little knowledge of economics.