It seems like an easy way around this is to sell gift cards and only allow gift card payment for the adult content.
The right solution is what they're doing - finding a sane payment processor to work with.
Edit for clarity:
Stripe came over to them and said "if you have NSFW stuff for sale, we will not process any of your payments." The majority of revenue for itch is SFW content. If they start selling them for gift cards or points or whatever, Stripe will cut their revenue to 0.
It makes no sense to rush development of an alternative stopgap measure that is worse financially for you than the status quo.