The thing is that much of the Bitcoin POS equipment being rolled out now can be updated to support various altcoins.

We will need to keep a close eye on the consumer side and follow demand. But I think there will be many coins in circulation eventually with a handful performing the majority of volume. Today people use Visa, Mastercard, Discover, etc. In the future they'll have options like, Bitcoin, Goldcoin, Dogecoin, etc.

Andreas Antonopoulos makes a similar prediction in the following presentation:

http://altcoinpress.com/2014/04/andreas-antonopoulos-cryptocurrency-is-a-language/