In my opinion I think start having a serious talk with her when she is not ....... Let her know you will be the best husband you can for her, and how much you love and trust her. Tell her about your fantasy to share her, and if she would do that for you it would mean the world and you would be so happy. You couldn’t ask for more. When you let them know how much it would turn you on and that you trust them. That will give her the thought that she could do it safely without jealousy and she has your complete approval. She will also know she is doing something great for your marriage. These simple things plan the seed. Everyone woman want a happy marriage. She will want to please you. Especially if you be a great husband to her. That is the key physiologically. I can safely tell you this because I have shared a few woman in my time.
I agree with HotAsianwife. The only way to convince your 'wife' to be a 'hotwife' is building trust with her and convincing her that the experience will only strengthen your relationship. But please don't give up hope. Take it from someone that was successful in this realm.
I first brought up the idea with my wife 6 years ago. Her initial response, "...that sounds like a great fantasy for us honey, but I don't think I could do that for real". Fast forward and she had her first experience a couple months ago. She absolutely loved it. But as you can see, it didn't happen over-night. On many occasions I had given up hope. Gave up more than once in utter frustration only to continue what I began to think was an exercise in futility. And it may sound strange to some, but for me, having a hotwife is not a kink but who I am. There were times I was thinking divorce.
How did she finally make the leap? Patience and persistence. I didn't give up, but I also didn't push too hard. I asked her about her reservations, her fears. For her, it was that it might somehow damage our relationship. I kept reinforcing over and over how this would only improve and strengthen our bond. How it would improve our sex. That it was an experience we would both 'share together' as a couple. Not just an experience that one of us (primarily me) would get off on. It may sound silly, but it's like teaching someone who has a fear of water to swim. You don't do that by throwing them into the deep end of the pool.
You start by getting their feet wet, so to speak. For us, that meant the fantasy being a constant part of our sex life. We never had sex without hotwife dirty talk and role playing - which she enjoyed. It sounds like your wife is very much into these role play fantasies as well. Start there. All women have sexual fantasies, even if they are shy or reluctant to share them. When you're having sex ask her and encourage and play along. My wife is a natural sub, so she has fantasies about being used for sex by men. It was an easy place to start. I also introduced hotwife porn into our sex so she would get use to the idea of two men/one woman. And, seeing other hotwifes getting ready for a date with a bull, and seeing their happy, proud husbands.
Eventually, all this piqued her curiosity and led her to doing her own research. She started reporting back to me about how hotwifing is a very common fantasy with many men. This normalized it for her. That it wasn't something weird, or just me. And it wasn't some sort of ruse for me to have sex with other women. And by participating she would be supporting me, being a good wife, so to speak. She also started watching her own hotwife porn, and reading hot stories from other hotwifes.
The final step was finding 'the right' guy. This also took time. It's a whole other obstacle. We used a few different methods and dating sites. Once you get your wife to set up a profile, it can be transformational. Typically, women will get swamped by guys trying to ...... with them - it can really improve their sense of sexiness and attractiveness. They will get turned on by so many guys wanting them for sex.
The final key for me was letting her post and find the guy that she was attracted to the most. With the confidence of knowing they are extremely desirable, coupled with the fact that they have your consent to have sex with another guy while in a trusting and loving relationship, it will allow her to take the last step - even if it's just meeting a guy for drinks knowing he wants to fuck her. It's extremely empowering for her.
It was a lot of up-front work, but by the end, it all went pretty fast. The week she posted she was really in the mood and feeling sexy. She got a flood of responses. She found a guy that she was really attracted to and they were able to meet in short order. They met for drinks to test the chemistry - and about 2 hours later they were in our bed naked licking, sucking and fucking. I came home to cum and sweat soaked sheets.
I cannot tell you how much it was all worth the wait!!!