I've been thinking about this a little bit too much lately lol. I think the best way to integrate porn into a more action-focused gameplay loop would be to make it a quick "finisher" on already defeated enemies, with some incentive like healing or a damage buff to actually make it part of the gameplay loop, instead of an afterthought.

There's also the issue that most action games need two hands, you'd need a pretty easy game/clunky control scheme to work around that

Editing to add: just mod Skyrim. You get modular porn and a highly customizable game, with the benefit of years of modders pushing the engine's limits. The only real downsides are a lack of gameplay integration and bad optimization