There are lots of coins this days and more are still emerging by the day. If eventually cryptocurrency becomes accepted globally and it's been adopted for usage, do you think all the coins would be accepted for usage or only a selected few?
Not all coins will be accepted. I think it depends on merchants or companies what coins will they accept as a medium of exchange once cryptocurrency will be fully adapted around the world. Not all cryptocurrency has usage, most of altcoins are shitcoins, created to make profit.