I think that cryptocurrencies are not to replace fiat money. It's not their main goal. They are a great alternative way to use and invest into. And as they are volatile, it's really difficult to see them being the world currency or the main currency of a country. And I'm pretty sure that they will stay like this in the future also.
Yes, indeed Bitcoin and cryptocurrencies will not replace fiat. However, Bitcoin and cryptocurrencies will not be like this forever, because every time Bitcoin and cryptocurrencies experience development which is a progressive rate of a powerful but not well-known technology.
I support Bitcoin to be more powerful, and cryptocurrencies are starting to become a mainstream payment tool, at least as an alternative payment gateway for those who want their privacy to be maintained.
Even though the digital era is growing, and online payment systems are increasing, it seems that cryptocurrency will not be able to completely replace fiat, but only as an alternative to payments. Yes, it is true, regulatory constraints are obstacles, but it is the right of every country to maintain its economic sovereignty. e-money can also be effective in online transactions.
but lately, there are several countries that have had a discourse to create their own cryptocurrency. I don't know if it's just a rumor or a plan to deal with digitalization and the rapid development of technology.
what is clear, cryptocurrency and fiat have their respective advantages, there is no need to debate which one will lead in the future. whatever is important is that we can use it comfortably.