A monogamous relationship rewards the husband with 100% percent of his wife's love.
100% of her respect.
100% of her compliments.
100% of her physical and mental enjoyment.
100% of her beautiful body is offered to you alone.
Bringing another man into the bedroom Math Equation, brings your share down to 50%.
Why lose a good thing? Why take a chance of your share going to zero?
Zero, when she dumps you for another man...or other men.
Zero, when she dumps you for showing how much you value her. NOT!
Fantasy's are great until they become reality. Passion follows Natures laws, runs downhill, as does rain. But rarely in a straight line.
You are not a Prophet. You do not know how this will play out.
Your Profit Margin is a faithful wife in a faithful marriage. Do not gamble with your most valuable asset. The better half with the boobs.
You really have only one option, and that's wait and see if SHE ever brings it up again. You never know. But ANY kind of pressure from you, even hinting to her that you're still into this, makes it somewhat unlikely.
Now that you have a family, it's almost certain these old fantasies and talk of roleplay have diminished or outright disappeared. Prior to having children (and presumably back when you two were in your 20's) these types of things probably seemed interesting to her, and worthy of consideration. OR it was all simply talk on her behalf, with no intentions of actually following through. Just a bit of dirty talk.
Best case scenario, you wait until you're empty-nesters to even mention this topic again. IF she's at all interested in it, it would be when the parental responsibilities have more or less ended.
If you simply can not wait and have zero restraint with this, then see if she'd be into something like chatroulette (webcam based chat). Other men or couples can then, safely and from a distance, 'admire' your wife (and/or you).
I have very mild exhibitionist tendencies - something I've never admitted to anybody, ever. They're not strong enough to act upon (in any way, shape or form, except with my wife. If she catches me masturbating, it's exciting to me, and she'll almost always join in), and it's something I rarely even think about, but they're there. My wife certainly would not have any interest in this, whatsoever, and I wouldn't bother to even ask, I just know. However, if I knew my wife/partner had similar interests, I would have no problem - as long as it's anonymous. Sites like those seem to cater to that demographic, in which men, women and couples can view each other, anonymously. Wearing a mask or manouevering your camera in a way which doesn't show your face, for example.
But again, if your wife shows NO interest in this sort of thing whatsoever, best not to bring it up. As others have said, she may view this as objectification (which it is).