Well if The Oracle says so, it must be like that
Jokes aside, maybe I got carried away by this new pacing of the game. Asking to be the best man/woman and organizing the bachelor(ette) party it is likely where it is headed.
The swinger thing it was more because they seems the "candidate couple" for that, especially after what we saw in the dressing room. And again I was suggesting that if it is the case the things will be set in motion in some way, not explicitly but preparing the field for that to happen either at the bachelor party or whenever.
The fact that they want to get married it doesn't mean that they are not into it, we don't know much about them but it won't be that bizarre they are into the swinging life even before marriage.