Earlier quoted context omitted.
I see, by issuer do you mean "Visa", "MasterCard", etc.? Because there are only a handful of those. > Plus, the population that is eligible for credit doesn't equal total population of the planet. True, I'm talking about a hypothetical "maximal usage" future.
There may be only a handful that are well known, but that doesn't mean that there aren't more possible issuer numbers available. The first six digits make up the issuer identifier, so there are 10^6 possible issuers. Sure, it's not ipv6 level address space (2^128), but ~10,000,000,000,000,000 possible card numbers seems like it should last many lifetimes, especially if you consider that card numbers could be recycled…
> My guess is the credit card itself as a concept will be long gone before the numbers are all used up.
I agree. Products like "privacy.com" hint that we could be approaching a "new number per purchase" meta. Even in that edge-case, if one million issuers get to have 10 billion numbers each, that would leave tens of concurrent purchases per person per issuer for an issuer with a billion users. A monopoly-level media site that lets you open a paid-subscription to multiple people could easily end up needing tens of concurrent cards per user. It seems like issuer-to-issuer number recycling would be required for sure.