I also noticed all the mentions of teasing and it stands out strongly to me as well. I get the impression from all those mentions that perhaps you are hesitant to really put this out there (hesitant about how she will react, the finality of it perhaps). So instead of bringing it up directly, talking openly and expressing your honest desire to actually go through with it you keep teasing her with it during sex and hoping that she will say she wants to go through with it. You are putting this on her shoulders; many women, even ones who actually want to do it, when it's put on their shoulders will do exactly what your wife has done. Get excited about it, seem like she wants it, but will never step up and express her desire to do it. Take control here, tell her you want it, explain to her that you're excited about her exploring her fantasies, about exploring with you, seeing her get so much pleasure etc. Talk openly about it when you're NOT having sex. Allow her to be able to actually go through with it, without feeling like it was all her idea (ie: she is to blame for it, or she is the slut for wanting it etc.).
Now, that very well may be off base too. Could be that she's just not really interested in it at all
