I believe that bitcoin will never replace fiat because fiat is a well organized money and fiat system is supported by every government around the world and each money that a country have has its history behind it.
No, it is not good to say the fiat is a well organized currency, as fiat is only a fiat used by the people and governments for their use only, the only thing is that it has a strong support, but not have any organized method for it to maintain.