The moment every country decides to convert to cryptocurrency, that is when the prices of all cryptos will just skyrocket. But I really don't know if this will happen in future.
maybe yes and maybe maybe not, I think there might be some countries not beautiful to cryptocurrency, for example in the country of Indonesia still prohibits bitcoin and crytocurrency as a substitute for money in Indonesia.
The whole world will use one digital currency and buying, selling would be easy. You will buy from your home and will pay your bills from your bedroom. These are the benefits of bitcoin and Altcoin. The world is gradually moves on towards digital things and cryptocurrency is one of them. You will not need to convert your money in the required one due to bitcoin.