I think the biggest issue is probably going to be the payment processing.Really, if this isn't already a thing, that's a massive amount of demand left...unsatisfied.
Wish I had the balls
Like was mentioned, PayPal had already made an exception for Patreon's adult content creators. You'd have to do something similar with a porn-specific sister site, which might be difficult if you're attempting to allow material that is prohibited on Patreon.
But man, the more I look at these terms, the more misogynistic it feels. It hits women hardest.