Cryptocurrency is just a fiat in a modern world. They can be distinguished in some nature but their uses and relevance are comparable. The good thing with crypto is that it is decentralised and cannot be controlled by one. It also has its fixed nature.
The "only difference" you talk about is a complete change to the current financial and monetary market, so it's not just a difference. In my opinion, centralized FIATs will not disappear for decades or even hundreds of years. I think cryptocurrencies will just take a piece of the financial cake and will exist alongside other forms of payment. Everyone will be able to decide which one they want to use.
While you are likely right that governments are not going to give up on the current financial and monetary system anytime soon, it depends also on the people living in that country. For large countries where the currency is used by many people like the USD or EUR it not going to change. But smaller countries where there is high inflation could feel a lot of pressure
. If the people in a country would just stop using the currency overnight and everybody switches to cryptos then there would be a lot of trouble for the government. While that might sound easy, I dont think it can easily work out like that, every one in the country witching to using cryptocurrency. Even now, if a statistics where taken of this countries that are already well engaged in crypto. how many %tage of the population are fully engaged in cryptocurrency? and also is it really going to be possible for any government to allow its monetary policy over run by cryptocurrency? I do believe some day in the future there is going to be a wider rand on crypto adoption but I still see Fiat as the main countries currency.