I think it's impossible to replace real money in digital currencies. Not all of us use bitcoin besides the fiat has the symbol of the identity of each country. Not all citizens of a country live with technology just like those who live in the islands or away from the city. Not all of us in the modern world are the ones who prefer not to follow. You do not have a transaction when there is no internet the fiat is faster when it comes to transactions. And more studies need to be done before they can be used for digital currencies. And it's not easy to change an important thing that's so easy and it's always used everyday