in my humble opinion btc will never replace fiat its just a coin that can be not copied or faked but speed of trades cant occur good and with general aceptancy if this coin never reaches atm good or a site like paypal to btc and bank in all in one and besides most of fiat rules the world and governements do acept it soo its fiat first then pay pal then others then btc into 4th or 5th forever i supouse