This entire situation is badly misunderstood all over the Internet. As the article itself states, alternative payment processors that are used primarily for adult content already exist. CC Bill was the example given. And they accept Visa and Mastercard. They're used by websites with plenty of explicit adult content, including simulated rape, incest, and "teen" porn. It isn't Visa and Mastercard forbidding this. In this case, it's Stripe, though it seems likely they're doing it because of pressure from Mastercard, which in turn received pressure targeting these particular platforms from some advocacy group in Australia. But itch.io and Stream could still use CC Bill, and customers would still be able to pay with Visa and Mastercard.

The reason mainstream websites don't use CC Bill and it is used almost exclusively for porn, is because they charge a lot more than Stripe and the more mainstream payment processors do. There isn't really a ban on this kind of material, provided the platform hosting it is willing to use alternative processors, so much as a price increase.

Even with Pornhub and OnlyFans debacles, they never hosted content that can't be found elsewhere on sites that allow you to pay with Visa and Mastercard. The reason those platforms were targeted was never the content itself, but non-compliance with rules that professional studios have always had to abide by requiring they keep copies of government-issued ID of all performers and provide those to any viewer who asks for it, in order to be able to prove they aren't accidentally hosting content with children or otherwise non-consenting performers.

Ultimately, if a website wants to host content with a guy taking a shit on his twin underage daughters, they can do that, and you can pay for it with Visa and Mastercard, as long as they use something like CC Bill for processing and they keep adequate records enabling them to prove the "underage" characters and not actually played by underage performers, and the people involved aren't actually related. Or, maybe more precisely, you can have real twins in a scene together, but you're then limited by byzantine country-by-country laws I have no personal knowledge of regarding what they are and are not allowed to do together that counts as sex.

The Internet is where nuance goes to die, so this all gets distilled down to "Visa and Mastercard don't allow you to buy porn" by the time most people find out about any of it.