Cheating isn't a productive solution.
You can't move forward until you find forgiveness. If that takes years, it takes years.
Opening your relationship up could help - but not if you're doing it for revenge. If you're acting out of anger instead of love, what is the point of being together?
Now, if you mean 'evening out the playing field' in terms of you being able to sleep with someone else because you want to and she already has, then yes.... perhaps you two can consider poly.
A quad is great in theory, but it's difficult enough to find a triad that works. Finding two people who are into each other plus you plus your wife won't be an easy job. It could happen, though.
If you're still at the heated discussion stage, perhaps now is not the right time to start though? You want your relationship to be in a good place before you start adding extras. If your foundation is rocky, it will crack under the weight of new people.
Can you tell us a bit more? What are the reasons for her cheating, besides just feeling that she's 'poly'? Can you recognise anything that you could have done better? What do you like about the idea of poly? Do you think you want to be poly? What stage are you at in your discussions about it and how long have you been discussing it? What are your heated discussions about and are you still punishing her for cheating?
me: open poly (31, female)
GF: (41, female) my long-distance, long-term partner
Earth: (35, female) newly dating
Hubby: (38, male) GF's husband
Garcon: (28, male) GF's boyfriend/submissive
“Peace comes from within. Do not seek it without." ~ Buddha