The thing is that even today, where it's "easy", still nearly nobody is writing code to directly support the six different credit card types. Instead, businesse

The thing is that even today, where it's "easy", still nearly nobody is writing code to directly support the six different credit card types. Instead, businesses mostly rely on payment processors. In a world where it's impossible to support all six card types directly with one codebase, one of the key dimensions on which payment processors would compete for mindshare, would be abstracting away those difficulties in supporting all six card types, enabling the business that uses them to accept more cards, more easily, than if the business went with some rival payment-processor. This would be a headline feature, however hard it is for them to accomplish internally. The only difference from today, would be that now, due to those potentially-conflicting requirements, the payment processors would have to build six entirely-distinct payment backends that don't share a data model. (Basically treating each credit card platform's cards as different "payment rails", as distinctive from one-another as credit card payment rails today are from debit card payment rails.) And then, of course, the payment processors themselves would come up with guidelines for handling those six different data warehouses and associated infrastructure, separate/downstream from the guidelines enforced upon each data warehouse by the associated credit platform... and those payment-processor-produced guidelines, might look again quite a lot like PCI-DSS :P