To me, Plot Without Porn means that the plot isn't about sex. There can be sex in the story, but sex shouldn't be the goal or the end-all-be-all. Which means that you can dance that fine line and have sex in your story and it would still be Plot Without Porn, but it's harder to do. I suppose the reason why people think of Plot Without Porn = No Sex is because it's easier to not include sex at all than to do so and not have it take over the story. Because sex is powerful and fascinating and intriguing.
So in thinking about this proposed Genderswap/Bodyswap Plot Without Porn Ficathon - I think that yes, sex can be part of the story. And honestly, it should be a part of the story because genderswap/bodyswaps are about exploring identity and a person's sexuality is a part of that identity. Just think of Faith inside Buffy's body when she's taking that bubble bath. But exploring sexuality doesn't equate to turning a story all about the sex. Moderation, right?
It seems like the question then becomes how do you write sex without it overtaking your plot. The answer to me seems to be have a plot that doesn't hinge on sex - i.e. if you're writing a romantic tale, sex shouldn't be the goal that fixes all problems in the relationship and ties things in a nifty bow. In my experience, sex only further complicates relationships, amplifying the problems between people.
But that's just my take. Anyone else care to weigh in? How do you define Plot Without Porn?