Itch.io is already seeking new payment processors.
https://www.rockpapershotgun.com/itchio-are-seeking-out-new-payment-processors-w...
So apparently they agree with me. :)
This is definitely good move but I am afraid it's only a temporary solution without some law changes, considering that while you can replace payment processor, you will likely still use Visa/Mastercard under the hood and by looking at Steam, those companies can still pressure you to do it their way. Plus you mentioned DLSite which has been exactly hit with the same thing and now a lot of the content is locked to japanese only consumer.
Pushing back against the Visa and Mastercard stuff may yet see results. They're already taking stock hits. For my part, I'm making complaints on the phone daily and I'm not the only one. The more people raise a stink about this in the proper avenues, the more payment processors are going to have to contend with the fact that censorship is not going to benefit their profits.
Oh yeah, definitely, the "louder" we are, the more power we have, so glad to hear that you are doing your part. Still would recommend also trying to push some legislation if possible (not everyone has that option but those who do should definitely use it), so that those companies won't be able to do so legally in the future.