Cryptos, or cryptos currency, is a kind of currency, so its ultimate goal is become the currency in exchange with other goods (like an apple, a pack of cigaret...)
I think that the most obstacle now is the speed, when you go to supper market, you want to buy a kg of apple and people is not patient enough to wait for like 3 confirmation to confirm the transaction, so the "instant confirmation" is needed. If cryptos in general can solve this problem, we can think of cryptos going mainstream.

You can say that we can use the buffer service, like VISA doing for the bank, but that we will go back to the decentralisation thing.