If you don't mind me asking, what exactly are you trying to achieve with that conversation? I take it your wife doesn't have really big boobs (or what we call big here) because if she did, you would've told her about your fetish a long time ago and you wouldn't have to trigger the conversation years after you met her for the first time.
I ask you this because I've learnt to be cautious with this subject the hard way. Let me give you a personal example:
My wife knows a bit about my fetish. It's something that randomly shows up between laughs in nights out with friends and things like that. She doesn't know the size I consider to be perfect or the fact that I prefer "natural" looking fakes (not bolt-ons). She wouldn't talk about it in a serious way because she doesn't like being a small B cup, but also there's no way she'd consider getting implants. She told me a couple of times and I don't want to push it any further. The first and only time she considered it in a very subtle and vague way, my heart started racing and I failed miserably at supporting her and her natural size (something expected from a loving husband), she got mad and I learnt to keep my fetishes for me.
I know some of you will have different stories with wives or girlfriends who actually get implants both for them and for you to enjoy, but this is the way it's been for me. Boobs have always been a status meter for women. Bustier women get more attention from everyone and less busty or plain flat ones feel, for the lack of a better word, "handicapped" because they don't have that natural power over men, so they feel bad, angry or overly defensive when the subject comes up.
That's why I'd be cautious about it. It's a tricky subject and, if handled poorly, can make your wife think you don't find her attractive, that you're looking for bustier women elsewhere, that you want her to get a boobjob even if she doesn't like the idea... things like that.