Original link which seems to have been taken down: https://www.vice.com/en/article/group-behind-steam-censorship-policies-have-powerful-allies-and-targeted-popular-games-with-outlandish-claims/
Update from the author:
a few ways to be honest.
They already have steam wallet cards at most electronic retail stores which operate the same as gift cards
but I was thinking more along the line of the payment processor is still there, but the goods being purchased is no longer the game itself, just adding currency on, which more-or-less removes the problem all together. Payment processors are no longer being used to buy NSFW content, its being used to purchase wallet funds. So the association is no longer valid.
Alternatively they could go the Mullvad approach as well, and allow for cash, check and wire transfer over if they really wanted to. Heck honestly like what PC said, with how big they are, they could even make a low transaction fee(seller side) savings card and could probably rival the companies themselves. I know a few people that would happily switch to said card if it meant ease of access buying games.
Additionally, a mix of these could be done, at some point card companies would fold because its threatening their bottom line. I personally think if they went the steam wallet route, the companies wouldn't want to engage big stores such as walmart, as a good portion of their revenue is via the transaction fees those companies provide.
this is all hypotheticals though