But who know's we don't know what would happen.
Nobody really knows what is going to happen in the next upcoming years. But I don't think so that bitcoin will ever replace fiat or dollar soon. The foundation of the economy of each country is depending on its fiat or dollar so I guess they will not risk their countries economy for a decentralized type of crypto currency.
But still all the prediction forsuch types of things are only time pass because the current position and reputation is under some doubt's for some countries to use bitcoin , Only few of countries accepted bitcoin as the legit money but some of the countries banned it and rest of them are confused to declare what about bitcoin