Sage? GoCardless? Coinbase? Etsy? A platform that pays out specifically for nsfw content (like pornhub)? Hatreon, as many have mentioned?

If no available alternatives suit, and there is a big demand for something different, someone passionate should go build it and get rich! And if there isn't a big demand for it, so be it! Not everyone gets to have a liveable salary from writing furry fanfic porn, c'est la vie. The entitlement in the letter really bothers me.