I think Tonberry hit on many of the points (and cautions) that came immediately to my mind too.
It IS a slippery slope. Once you start there's all kinds of directions it could drift. Some of those could be wonderful - some could be disaster.
Maybe the most important thing to remember - and plan for - is that if you and she really clicked in bed, more than likely you'll both want it to continue. And THAT is when it get's tricky.
I don't know your wife. And maybe there's these type of pieces YOU don't know either. Fantasy is one thing - reality often different. We might think it would be all innocent fun. And maybe, if it were a total stranger at some place we'd never see again - it could be. Doesn't sound like the case here.
IS your wife a 'thinker' type ? Maybe you should engage the thinker about all the directions this could take. Then see how she feels.
I also like what Tonberry suggested about a kiss when all together. Not just a little peck. A nice long,deep tongue kiss, groping hands etc. THEN see how we all feel about it ?
Your wife might well be the type to want to offer you something hot for a little variation. I can be a good feeling to do this for someone you love. But you need to play the part out to the extreme - because there's no telling it won't go there once you start. The sex chemistry. The love that might develop. More of a full sharing in each other's lives. Play the scenerio out to the max and all see how it feels.
Just in case............