There are already other credit cards out there: namely Discover and American Express. Both operate somewhat separately from Visa/MC, but are forced to share the same network (First Data). Introducing a new credit card won't make a difference, because it'll have to use the same network.
Groupon and PayPal, and just about every other consumer oriented brand that "accepts" credit cards is just re-branding some other service and tacking on some more fees. Groupon certainly is not building a credit card network. More than likely, they're not even creating a credit card gateway. It won't have any impact, whatsoever, on the industry, as per the original post's suggestion.