As someone who does have a mono partner who has made it work well for 2 years I will say R sounds like poison. He wants his cake and eat it too. To be honest he could be looking to build his harem.
You guys have a serious lack of time. Honestly I do not think while life is so and quality time constrained is not the time to add more commitments. Poly has the habit of illuminating every crack and flaw a relationship has.
I am an INTJ female. While I love fiercely talking about my feelings can be torture and hard to express. But I have learned that I need to communicate with Butch and listen to his side too. He isn't a mind trade. I would ask your wife if she us willing to risk your relationship for R.
40 yo straight female
Married in the eyes of the government to Butch since 2001...
Murf my monogamous second husband has been with me since May of 2012.
In a V relationship with an average 60/40 split of time. Only due to Murf's and Butch's crappy work schedules.