You sound like you have a deep compassion and understanding for your wife.
I think that what you are going through is perfectly natural, given your/her exploration with poly for that one year and the fact that you have never fully experienced another woman. I have been there and I understand the desire to explore others.
How to talk to her... As others have said, the conversation will go as it goes, but there are perhaps some things you can do to help.
Firstly, just take the time to remind yourself that it's ok to raise the discussion. That's all it is. A discussion. You want to share something that's on your mind.
This is a good angle to come from. If you express that you want to share something with her and explore your feelings with her through a discussion, it will help her to feel involved. If we feel part of the same team, we naturally feel less defensive and more involved in our partner's life and thoughts.
It could also be a good approach to say that you have been thinking about the joy you felt for her when she was involved with someone else, and that you would like to have her insight into what that feels like - what she enjoyed about it and what she didn't.
Having the conversation will be the first step and the rest will naturally follow from there. If she does seem open to the idea, my advice would be to give her the opportunity to build her own strength and self-esteem. My advice would also be to pace it and, most importantly, ask what she needs. I'm really a big fan (in these situations) of setting 'review dates', i.e. in 3 months, we'll revisit. During those 3 months, you don't date, but you read polyamory books, research, work on your marriage, work on your compassion while she works on her confidence, etc. It could be that you agree to check in every 3 months, but agree that no dating will happen for 1 year. Whatever arrangement works for both of you is the best arrangement to make.
Good luck with your discussion - let us know how it goes!
me: open poly (31, female)
GF: (41, female) my long-distance, long-term partner
Earth: (35, female) newly dating
Hubby: (38, male) GF's husband
Garcon: (28, male) GF's boyfriend/submissive
“Peace comes from within. Do not seek it without." ~ Buddha