I dont think bitcoin can replace fiat money. Fiat monetary standards enable the government to have a lot of control of their economy.
They can choose to print progressively or remove some from the economy through banks. A cryptocurrency would need to be connected to their fiat cash and be absolutely controllable, for a government to permit it instead of their fiat, however that would essentially be a fiat at any rate. So we would require new enactment or new governments.