well its too bold to say fiat is useless and going to fail. I just believe why bitcoin or altcoins is future cause they seems good and could turn out to be a currency for transaction but i believe it would be true cause human live is keep developing and this technology is really good to be use for transaction. Despite all of good reasons there is a real problem with cryptocurrency, crypto are to volatile and too complicated for some people. So i believe many people would stick into fiat currency.