Though, crypto supports are hopeful that one day cryptocurrencies will replace fiat currencies but this is not possible because various governments are mulling to issue their own cryptocurrencies which will have legal status and people won't hesitate to use them because of governments backing. Also, cryptos have many inherent flaws without addressing them it is not possible for them even to co-exists with fiat currencies. However, this situation may be changed if developers will be able to address these problems.