I have traded Bitcoin and Ether in the past. I believe cryptocurrencies are here to stay but I find it unlikely they will ever fully replace fiat currency. People will want to always know how much an alt-coin is compared to USD. However, digital currencies might dominate online transactions in the future. I believe Ether or perhaps EOS (shout out to Dan), will overtake Bitcoin in the the future, because they are more practical to use on a daily basis.