The global economy is nearly 80 trillion USD per year. Payments using any type of cryptocurrency as a medium of payment is a tiny fraction of this total.
What are some of the reasons preventing cryptocurrency from being more successful as a medium of payment?
first of all cryptocurrencies are not enough fast for payments. it takes time for approvement. especially for bitcoin. second volatility is very high so there is a risk for both buyers and sellers. third it is still not easy to cash out from cryptocurrencies because of some regulations.
Cryptocurrency can move any amount of money from anywhere to anywhere in moments for essentially no cost. So, I'm skeptical that speed is an obstacle to widespread use.
Now, some cryptocurrencies such as bitcoin and ether are too slow for payments as both have a low transaction rate (less than 10 transactions per minute) and long confirmation times (bitcoin takes nearly an hour). Other cryptocurrencies are better suited for payment because they have higher transaction rate and shorted confirmation times.
And, perhaps there will be a new cryptocurrency designed to have extremely high transaction rates... much higher than card interchanges such as Visa International, and where confirmation happens within a few seconds.