I think friends definitely play a huge role. It kind of sets the tone for what's normal and determines what kind of opportunities might naturally arise.
For my wife, one of her main hangups is that it "isn't normal" and she feels afraid to do anything. I don't think she will ever agree to be shared as a result of deliberate, advanced planning of an encounter. It would have to happen naturally in the right environment.
She has one more boring group of married friends she goes out with regularly. They just go to dinner and that's typically it - nothing really happens.
On the other hand, she has one pretty wild friend who is now divorced and, unfortunately, a second friend that always hangs out with them together, who is kind of a goody goody. They got together last week and ended up going to a strip club after dinner, where they got chatted up by two men. At the end of the night, the wild friend went back to her house with the two men, while my wife drove the other friend home. Allegedly nothing happened between the wild friend and the two men but who knows. I have a strong suspicion that if the 2nd friend wasn't relying on my wife to drive her home, that my wife would have ended up going back to her wild friend's house for a couple drinks with the two men. I'm sure she would go into it thinking she was going to be good, but who knows what would happen after a few more cocktails.
This is a screencap from a video her friend sent her, which my wife did not actually show me but I noticed on her phone when I went to fix something for her (and obviously snooped around). She had told me she danced with her friends in the back of the club and she told me about the guys but she said the dancing happened before the men came over. In the video you can hear a man laughing / talking and I'm pretty sure one of them took a picture of her at one point because you see a camera flashlight light her up for a second and she turns and makes a surprised face while smiling. I can't really be certain of anything from the short, blurry clips but I think she decided not to show me these because she was afraid they might be incriminating.
So I think if your wife has a wild friend like that and enough of those sort of opportunities arise, maybe something will eventually happen. The chances certainly seem a lot better, at least. Of course, the problem is, I'm not sure this is exactly how I'd want it to happen... At this point though, I'm not sure how upset I'd be.