They will become more popular as the cost-effective convenience they have provided. National currencies will still exist as a nation depends on its currency to define its boundary, values, goods and policies. The same principle applies to languages.

I believe crypto and fiat will co-exist in the future, and that crypto will probably be equally liquid over time. Crypto and fiat currencies will compete to provide greater transparency on minting, burning and the intrinsic value of the currency.

Initiatives like Facebook Libra and other company or consortium backed currencies will take us towards this future.

due to advantage of cryptocurrencies as compared with currencies.It may dominate the market.

Crytocurrencies have a lot of advantages but also several disadvantages. I do not consider volality as a major problem, since it will decrease if the market capitalization goes up. The biggest potential obstacle, however, is legislation. If cryptocurrencies become a serious threat for fiat money, governments and central banks will start to fight back and will potentially try to outlaw cryptocurrencies. It is simply a question of power.

Horst Treiblmaier In what perspective that it is considered as a threat for fiat money.

Quan Hoang Nguyen Central banks have a couple of policies at their disposal, such as setting interest rates, re-lending, re-discount, open market operations and credit policy. If citizens are using cryptocurrencies instead of national money some of these policies will not work as intended. In other words, central banks (and governments) are losing power.