Correct. The problem lies in a country that doesn't accept bitcoin, that's what makes bitcoin cann't replace fiat. However as an alternative, bitcoin very reliable than other payment processors because bitcoin easy to use.
And even that country is willing to accept and adopt bitcoin on their economy still it isn't sufficient to make the replacement of fiat. Fiat is needed and bitcoin is just another way of paying transactions and services that we are purchasing. I doubt it that it will be replacing the usage of fiat because it's decentralized and would you think that a centralized government will let something decentralized to be use as their main currency?
You think in wrong terms
You think in terms of major fiat currencies such as the Swiss franc or the US dollar, but there are plenty of other currencies out there which are devalued now and then. It is not about decentralization of course, it is about preserving the purchasing power of the value you obtained by spending your time and effort in the past. And don't be too optimistic about centralized governments either since these get overthrown as often. I'm curious which country would be the first to accept Bitcoin (or some other cryptocurrency, or a basket of cryptocurrencies) as their official money on par with, say, the American dollar. I've heard Roger Ver was going to create a Bitcoin state. I think he would do a lot better if he just organized a coup d'état in some country and grabbed power there
