If you can make it happen and it would bring you and your wife some good happy times, then absolutely go for it.
That is a form of it, yes. Gender really doesn't matter in some cases, just that the one partner is denied the priviledge of access while it is given to someone else outside of the marriage/partnership. Again, it's all about context. My suggestion if you want to know more about it is to hit up google, because you would find a lot more information on the topic, quite a bit of it not really good for discussing here.
As for the OP, dude it is a great thing if you want to open your mind up to various possibilities and share them with your partner. However, coming from a person of experience that if your partner is uncomfortable with your idea and/or fantasy, it should remain just a fantasy. It takes a lot of trust and understanding to go outside of the partnership, and I'm thankful that I actually searched for this in a partner before actually becoming seriously involved with them.
Always remember: being open-minded is a one-way street, but performing open-minded things require an all-access road.