I agree with these comments, your wife is hinting of a polyamorous relationship, even if just sexual, and feeling you out about it.
Some background- Prior to deciding on my wife, I was polyamorous. I had a few girlfriends who all knew about each other, and I only had sex with them. She was one of them. This was the way things were for years, and she was really the one who I was with the longest (these girlfriends would normally last 4 months to a year then we would break romantic contact for whatever reason and remain friends, in most cases anyways). Well she wanted to go monogamous with me and I wasn't ready, so she fell in with a monogamous guy in a different state, broke off relations with me though we stayed friends.
About two years later they broke up, she moved back to this city to be closer to her family and we ended up crossing paths/hanging out again. We got back into our poly relationship, I lost interest in my other girlfriends, and she lost interest in her girlfriends (one of whom was a mutual lover of us both though we never dated or had sex as a threesome), she had no boyfriends other than me. We made the decision to be monogamous, get married and start a family, leaving the option of including another permanent woman on the table (at her insistence).
The other women never materialized, I have no interest in it though can't say I could not at least try to be open to being committed to two women at once. We have very clear and well defined rules for this, it has to be her that brings someone else around and she has to communicate to me that this woman is a 'potential'. There have been women she met online, a couple we met in person but it always fizzled out really quick. None of the friends of hers that I am talking about are what she calls 'potentials'. I think they are more like 'pretends'.
Do not do it if it is not something you are emotionally and otherwise philosophically opposed to, as it could do harm to your relationship if you are left with feelings of resentment or guilt (all joking aside, this is very possible regardless of all joking of the "enviable" position you are in). Even so, proceed in your communications with your wife with these assumptions in mind, that it is her fantasy and you perhaps to either move forward with it in due time, or be prepared to explain very lovingly but firmly why you will not.
I am neither philosophically or emotionally opposed to the idea of any of this, but I can see how bad things could happen easily. My wife prefers women sexually and emotionally to fulfill what she wants from a beta type personality, but she NEEDS a male to fulfill what she wants from an alpha personality.
She expects me to be alpha 24 hours day 7 days a week, she demands it. But she has her own alpha mode and that of course doesn't mesh well with mine. hah....writing and thinking this out I am learning things about her and us. This explains why it seems like sometimes I can do no right, she wants me to be dominant but she wants to be dominant also.
I THINK she wants a second female in the relationship because that is someone from whom she can get her beta fix from while being dominant, meanwhile she can be beta to me and enjoy my dominance over her.
Either way handle it in such a way that your wife is knowing she is number one to you and you should be just fine.
I wish you well.
Thank you very much for your reply and kind thoughts. I let her know every day, in many ways, and in no uncertain terms, that she is #1 to me.