I'm pretty sure if someone came around offering adult only services for BTC it would not be forbidden in the services board.
I remember more than once an account claiming to be a girl posted a thread in the Services board offering pornographic photos and videos for sale. I don't know if there were any reasons preventing them from continuing, but it certainly wasn't forum policy.
I took some time to search in Services board for some of these topics, but unfortunately, I wasn't able to find any. However, I was surprised by how many cryptocurrency projects in the porn niche. Many projects remained active for a while before disappearing, and of course, not due to forum policies. Some of you maybe remember Sexcoin and xXxCoin and many others.
Porn could benefit from cryptocurrency use but from my understanding the porn watching crown isn't that keen on spending money in general, or especially going through hoops to watch their porn.
There have been many attempts to tie crypto to porn and most famously pornhub tried to turn to crypto only through a partnership with altcoin Verge:
https://www.theverge.com/2018/4/17/17244916/pornhub-cryptocurrency-verge-xvgWell, they still had to find partners to help them accept visa and mastercard because to this day not many of the users have figured out how to spend crypto...
As per OP, this forum might be an unusual place to stumble upon anything adult-oriented. This is a good example of how indifferent the two interest groups are to each other. And it's not as if us crypto users aren't consuming porn but we'd rather spend our coins on other things.