By the way, I initially missed the point of this post.
Personally I don't believe boycotting would work - I'm quite confident NSFW content provided the platform plenty of visibility and profit.
I'd rather chase them up to check what's cooking (if something is cooking at all) to restore the platform to a decent state.
And, VISA and Mastercard should publicly state WHAT is considered legit and what does not incur into "pressure".
I doubt they're going to take any action at all as they have little to gain and all to lose - so I believe the petition is our best bet so far.
(unless it gets shot in the foot like the Stop Killing Games one, by personally attacking Ross >_<)
Listing Itch.io alternatives, if allowed by Itch.io TOS, could be a good starting point tho.
VISA and Mastercard should publicly state WHAT is considered legit
The only entities that should have some say in what is legit and what not, is the ... well ... how do we call the law makers in a country? Those people. Has something to do with separation of powers. That separation is screwed up anyway in some English speaking countries, but that is another discussion.
So, corps should not have a say in this at all. Not even a tiny bit. They are infrastructure. Vital infrastructure. Arbitrarily denying services is abuse of monopoly and should be illegal.
Itch is very liberal, in case you have not noticed ;-) You can link to any other game platform and social here, on your profile, on your game's pages. But they kindly ask to not just make a game page that links to other stores. And they threaten to delist the page.
As for those credit card companies. I do not know exactly why they do this. If they fear legal consequences, those should be dealt with. If they support the agenda behind this, there is little hope. If they were bullied into this by thinking the facebook mums and Karens would cost them money, telling them in no uncertain terms that alienating adult consumers will lose them more money, might work. That change petition has 180k signers already, which is impressive for such a fringe nieche as adult indie games.