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 agreed on Bitcoin not to replace fiat currency because thats the purpose of it creation but that doesnt assumes it potential not to exceeded fiat or any other coins will have now or that will be mint in the same rate and the last time I checked there's no way such coin will exist.
Mind you, a lot of influential people and the institutions predicted Bitcoin to be double but now they are among Bitcoin investors and this shows Bitcoin is not just an ordinary coin.