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
The main reason behind stopping people from using bitcoin is that they have never heard about bitcoins and that goes to developing countries and the third world countries, where they are totally dependent on banking system and are not ready to accept the change or innovative things