What does she say now when you bring it up??
(Welcome to the board, by the way. The cool kids hang out here!)
For a long time, I felt it was very intriguing ... and sexy ... all of that. I had to feel secure enough in our relationship to "go there." And Mr. Fun knew that. So we talked (no pressure) and talked about fantasies we both have which require more than two people. And even as we were walking out the door to meet folks for the first time, he'd say "you don't have to do this you know. Don't do it for the wrong reasons." Even the first couple we had fun with -- we met at a restaurant and we were all ready to take the party someplace else, in the car, he was wonderful about making sure I was OK with everything.
HER feelings are what are important. From what I see (and guys, correct me here if I'm wrong), the women really do drive all of this. In fact, I do most of the communications with potential playmates now, etc. Just works best. (Keeps him from saying silly things to others)
So -- keep on talking; have fun discussing fantasies, etc. But, if at the end of the day she's not interested, you've learned how to have meaninful discussions with your wife and hopefully your relationship will benefit from the openness of conversation. It's all good.