I hope they figure out how to include everyone in their service, rather than a discriminatorily chosen group of people at their payment processors' whims.
Meanwhile payment processors are okay with 'filth' at every other level of their businesses -- don't paint them as wholesome, they're just legally cautious.
Also, for the sake of this discussion, let's re-evaluate what adult content is; it's not just pornography.
3. Game of Thrones, until the unfortunate last season, has been one of the most successful ever, and it was notorious for "adult" content (read: sex and violence). It is mainstream.
So please get off the high horse, there is clearly enough demand and acceptance of "adult" content in mainstream culture.
Individual artists would benefit from the ability to get paid in the case they don't luck out and get HBO to back them, though.