No I don't think it will replace fiat as the governments just won't approve due to the lack of control they can have with Bitcoin. But hey I can be wrong, anything can happen in this strange little world.
I like your open mindedness. I will just remind you quicky, don't forget American govt. tried to control the circulation of gold in the 17th century and placed some policy to limit its distribution.
Morale lesson: Nothing great comes through easily, without criticism and scam about it.
I can bet, countries like India and Pakistan will end up having there own government issued cryptos. If they back it up with wealth and purpose it would challenge at the top three and elevate there economy.