Yes, I also entirely agree with you Fiat can not be replaced fully as far as I think because still, a huge no of the population is not like the cryptocurrencies because of their high volatility they avoid them and a common man does not want to take a risk he wants a simple and peaceful life even some people are satisfied with the current system so they don't like the changes and yes when cryptos will be widely used as a legal tender more and more people will adopt the cryptocurrencies without fear.