Bitcoin will never replace fiat cash. A coin everyone mints at the same rate will. It will also replace bitcoin and all of the shitcoins.
Mark my words.
Bitcoin runs off the fumes of fiat.
I don't think that replacing Fiat is one of the objective why satoshi created Bitcoin mate because if that's the intention then maybe the governments around the world already banned crypto but it is not,meaning They still believe that this is just another Electronic payments but decentralized that's why they are avoiding to adopt.
Combination of crypto and Fiat will still best to Help the world and not being replacing each other.
And me ?i don't like that idea also because Fiat is needed same as crypto.