This question has been circling around the forum for a while now. To understand first on whether bitcoin can fully replace fiat, we must consider several circumstances affecting this change to all countries.

First, the fiat system has been around for ages and it is considered as the main medium of exchange. Before, the barter system was implemented but it slowly transgress to paper money in order to have a standard unit of exchange. The value of such currency per country also depends on its economic condition, gold reserves, etc.

Second, due to the present economic differences among developed, developing and underdeveloped countries, the first two can quickly adapt to this kind of change since they have the necessary technology to transition to a digitalized form of payment. On the other hand, underdeveloped countries who lack the necessary technology and advancements will be left behind from this change. This would technically further weaken their state, thus hampering the growth.

Lastly in order to implement a digitalized form of payment whether via BTC or a digital currency, all or at least majority of the countries must concur with this change. If some countries change their fiat system while others do not, this will create a conflict on which currency should be followed.

In spite of everything, I also believe that this change will be inevitable in the far future where technology will run the world and dictate our future. But for the time being, I cannot see bitcoin or a digitalized currency replacing FULLY the fiat system.