I'll admit that I know absolutely nothing about hotwifing, but in the version I've played thus far, not one other man has nutted in her, nor has it ever even been discussed.
- Is the husband okay is another man cums in his wife?
- If she's impregnated, does she bear the child?
- Will the husband assume the father role?
- What if the other man is black?
- How will the couple explain while they are both white, their child (the offspring of a black man other than the husband) is brown?
What's wrong with letting the wife determining whom she wants to date naturally, i.e. not using a swinger's website. Why not just have the husband tell her, "If, in your daily life, you meet another person (man or woman) you feel you'd like to have sex with, do what your heart tells you and as long as you tell me afterwards, go have a quickie during lunch or whatever"?
Also, many choices in the VN could/should have a third option for the wife to turn down the offer. Otherwise, it feels like the husband is trying to make yes/no decisions for her, instead of letting her choose for herself.
P.S.
If you decide not to remain 100% grounded in realism and think you'd like to include incest into the mix, you could. "Honey, I've always had a thing for my brother... do you think I could have sex with him, too?" or "Sweetheart, __________ (their son) has been flirting with me and I think I'd like to reciprocate. Would that be okay with you?"