Now, I think people are going to be able to spend cryptocurrencies, like Bitcoin, in mainstream situations. Cryptocurrencies will eventually replace credit cards and will be something you can access on your phone. I actually think cryptocurrency will replace fiat currencies entirely.
fiat currencies are centralized currency so government should monitor and controlling the fiat currency. But Bitcoin is a decentralized cryptocurrency and it is not control by government so cryptocurrency is not completely replaced in fiat currency may be it is legalised in future and fiat currencies will never stopped in entire world.