Of course, cryptocurrency can never replace the traditional national money of states. State governments will not allow this. And cryptocurrency by its nature is not capable of this. Stable coins can partially displace fiat, but state cash should remain. Even highly developed states with a high level of income of citizens who want to get rid of paper money will still use their non-cash money.
Never say never. Let's not forget one thing - there is nothing infinite in the world. The state and social foundations that exist now can be completely reformatted and changed within one decade.
We do not know what the world will be like in 10 years, everything will depend on technology. If we move into a fully digital era, then there will be no point in fiat means, they will also try to go into a fully digital environment, but during this transition there may be problems that simply destroy the fiat in the form in which we know it.
If one really looks too far into the future, then perhaps nothing is impossible. To date, such a situation has developed that most people are not ready to accept cryptocurrency for everyday use as a means of payment. In addition, it is necessary to take into account a significant part of elderly people who do not understand and do not understand the very essence of cryptocurrency and its capabilities, while no one will learn how to use it as a payment. therefore, in any case, for the full implementation of cryptocurrency to be used as a means of payment in order to replace fiat funds, at least two generations should change.