its impossible right now because there are alot of people who dont have internet connection most of people who dont have them are poor people and there are still alot of poor people in this world who cant even afford food and bitcoin unstable price made it impossible also government doesnt have control bitcoin they would refuse fiat to be replaced.
Yes it can be happen but,.not at this century because the whole world is not ready for that, this time we can see that every individual in the society has different levels of understanding of what crypto currency is; and how it works and still it is hard for a government to adopt the system much more on a developing countries that are not yet fully exposed to a digital world, imagine life without real money.. can a beggar on the street still beg a little amount from the by passer? or a side walk vendor can still sell its little goods? and if she can then how about the payment procedure.. i think that simple question alone makes crypto currency hard to replace the real money.
Crypto can replace fiats only when their value is stable and not so volatile. As of now crypto is only an investment not currency.
I'm seeing a lot of posts mentioning that the chances are low but possible. I'll have to completely disagree, it's simply not possible for a variety of reasons, price volatility and uncertainty are some of them but not the most major ones. Bitcoin is young, modern Fiat currencies, based on the capitalism concept have been established since forever and are widely used across the globe.