I think that the pregnancies being treated as a fetish more than anything, stems from the fact that Diane's story line was the first pregnancy related story, and that culminated into what essentially amounts to Diane and the MC running Summerville Breeding and Dairy inc.
Now, while monogamy is strictly a cultural phenomenon, I find your characterization of "women find it normal to be one of several wives or concubines" more than a little problematic. Women in cultures that have been traditionally polygamous, are also, with the exception of some tribal cultures, living in highly patriarchal cultures where most often patriarchy stems from a bullshit religious tradition that automatically assumes women to be second class and essentially property of men. So a statement that "women find it normal to be one of several wives" is just as problematic as claiming that women find it normal to wear a burkha in ISIS or in Iran. They've never had a choice in the matter in the first place. The fact that women in cultures that are traditionally polygamous, find it "normal" doesn't mean that it's because of their free will, but instead because of cultural and religious indoctrination, conditioning and oppression.
Personally, I really don't need DC introducing any cultural concept as backwards and idiotic as any of the more commonly known polygamous cultures or traditions to provide background to essentially fucking around. At the end of the day, we're talking about a game here, and to me a game that doesn't have any specific historical or cultural setting aside from generic western/north American town, doesn't need a cultural concept forced into it to justify the MC knocking up half the town.
I'm afraid you don't understand what I'm going at all. It's not about introducing some Arab patterns to the SS. Far be it from me.
The thing is to place such a culture somewhere near the town.
The very awareness of this and the upbringing of the SS heroes together with the knowledge that something like this exists and is doing well is enough to make them more open to such a possibility.
Personally, I thought more about the Native American tribe, in which one practiced not so much polygamy as the lack of a traditional family. I even prefer the matriarchal system there.
Let's say that as a result of consuming some local alcoholic products or plants, men quickly become imoptants and the tribe created a system to survive that older women rule there, and fathers are young men ... for example teenagers who have relationships with many women.
Something like this can be implemented without major problems. In the most economical version with new content, it is enough to add a book describing this culture and that, for example, Miss Bissette in the lesson would have students read it as something that will familiarize them with local customs. Suffice it to add that this tribe has a legend about a "chosen one" who is immune to this incoming infertility, that he appears every few generations and saves this tribe because he is extremely prolific, all his children are healthy and strong.
That women who are in a relationship with him live long, healthily and happily as long as they are ready to share it with other women, and you can recognize him by the fact that he has exceptionally handsome masculinity and is always ready for sex.
Let the "whispers" start circling the school and town scene with Judith and Annie in the locker room that MC is the chosen one from tribal legends and you have everything covered. You've explained why so many women want him to be the father of their child. Why do so many women want to be in a relationship with him and why they accept his relationship with other women.
A good idea is the basis for almost everything.
Islamic harems look bad in modern Western climates, but culture (made up), but referring to the indigenous people has a much greater sense and looks more attractive.
I know that some do not need such things, but I think that most people prefer such things than leaving loose ends that look meaningless.
