Cryptocurrencies will replace the traditional money in the future. It will be less controlled than traditional money. On the other side, it will be easier to use. People will use it as an instrument of transaction and not as an object of trade and speculation.
What makes you think that crypto currencies will replace fiat currency? Have ever thought of other third world currencies where internet access is limited? If crypto currencies take over as the only currency, then those countries will be neglected more and will eventually cease to exist. Crypto currencies might take over, but that will happen after dozens of decades, after hundreds of generation. But until then fiat and crypto currencies will prevail side by side.