As I understand section 132, there are two basic ways that a man obtains a plural wife. The first method is by choice, and the second method is by commandment.
If a man wants to marry a plural wife by choice, then he must have the consent of his first wife. If a man is commanded to marry a plural wife, then his first wife has no right to prohibit the marriage just as the man would be obligated to accept the marriage.
One thing that I cannot make out is how a plural marriage by commandment can reasonably establish mutually agreed upon duties and parameters for the relationship. When a marriage is mutually agreed upon, then a couple can be imagined to define their own expectations for the relationship. When a marriage is commanded then obviously that commandment is intended to be more than a formality, but what concrete expectations (duties) are placed on each party? Without any well defined parameters it would seem to me that either the husband or the wife might feel free to contribute nothing to the relationship while enjoying the contributions of the other party. If a man, for example, is commanded to take a wife, he might likely feel obliged to provide for her and she might easily decide to let him do so while offering no domestic support whatsoever, or any other kind of effort that might help to make the relationship anything but one-sided. Were a wife who had chosen him to do that, then he might feel justified in divorcing her or restricting his support, but when the Lord has expressly commanded him to take a particular wife, he cannot feel as free to pull away from. The relationship.
I would expect that duties and obligations do exist. It is clear from Isaiah 4 that traditional roles do not define those duties. The most fundamental purpose of a marriage relationship is reproductive and sexual. So we might easily imagine that the only firmly established roles and duties and expectations related to reproduction and sex. Indeed, in keeping with that reasoning, section 132 only seems to define sexual and reproductive relationship parameters. Still, this parameters are defined loosely enough that it is hard to imagine that they are complete.
When I marry a wife now, we can discuss ahead of time how many kids we want and how much sex we desire. We can discuss who is to have what responsibilities and how money will be spent. If, after 3 kids, she decides that she's done, but I want 3 more kids, I might feel justified in divorcing her. The Lord seems to solidly stipulate little more than that she is forbidden from sleeping with anyone else.
Maybe that's all there is. Maybe the husband is obligated to make a good faith effort to impregnate an assigned wife, and take what pleasure he can in that, so long as she wants to get pregnant, and then she is obligated to not go elsewhere to get pregnant. They would then only have more of a relationship than that if they both wanted it; a minimalist marriage. (Could be financially dangerous if she's inclined to get into debt.)
It's my hypothesis that modern changing attitudes towards polygamy are primarily driven by competition between women; either competing for the best men, or desiring to capitalize on the adoration of multiple leftover men. Women are both getting more picky, as they become more powerful, and the quality (and fertility) of men has been decreasing since at least the 80s. The male sex drive has pushed for polygamy for a long time, with no success, but only recently have polygamous families found an adoring audience among women. I identify this trend as being related to Isaiah 3, though I expect that in rather literal fulfillment of Isaiah 3, there will be a catastrophic war which destroys a huge portion of the male population.
There are two issues that lead me to suspect that section 132 is incomplete. First, it is pretty confusing. I think that what it lays out makes logical sense from first principles, but seems to leave some unanswered questions and seems to lack details that would connect the ideas together better. Second, Section 132 explicitly states that it lays out the laws governing concubines. This would seem like an especially hot button topic, as the word "concubine", at the very best, would refer to something like a wife, but with lesser status or rights of some kind. At the worst, the word describes nothing more than a sex slave. Although Section 132 starts by claiming that it will provide the laws governing concubines, it does not, leading me to suspect that the version we have today was bowdlerized. ie. I suspect that a version which did describe some kind of lower-status wife-like relationship existed, and that it likely contained information that would have connected the other ideas together better, but that it was edited out for publication, because it would have been received so negatively as to be a danger to the church. This would be very much in line with the history of the polygamy doctrine. I would suspect that the church as a whole needed a framework for one and not the other, so we only got a need-to-know version.
Why would the Lord permit such a thing?
Marriage is a fundamental prerequisite for exaltation. Based on our current revealed understanding of marriage, women would seem to have a significantly greater opportunity for exaltation than men, suggesting that women, by and large, are more valued than men, and inherently more righteous, on average. This is sometimes even semi-jokingly suggested by General Conference speakers. I do not think this is likely to be the case. I think that the Lord values both men and women. Nevertheless, genetic evidence suggests that many men have historically been unable to secure partners for reproduction, while women have been more uniformly successful. In Isaiah 3, we find that because of the wickedness, of the men, that many of them will die in a war, and then in Isaiah 4:1 we find that 7 women will take hold of 1 man. We might naively think that since the women will largely survive, that they were more righteous than the men. Nevertheless, that is not how the Lord describes them. The daughters of Zion are also described as wicked. By our current understanding of polygamy and exaltation, this would seem to imply that while the wicked men are killed and get no chance to marry, and be exalted, the women, on the other hand, will marry and have a good shot at exaltation, and hence, we might imagine that they are considered more worthy for exaltation than the men. (Yet both were described as wicked.)
What is the fundamental flaw that makes us unworthy of exaltation? We know that the detail that prevents exaltation is a failure to be sealed to a spouse. I would argue, from my observation of the dating markets, that there are many men, and many women, who are so inflexible in their gendered ways of thinking, that although they are sexually attracted to the opposite gender, they cannot abide the opposite gender well enough to commit to a direct relationship with them. These would be a large portion of the cat ladies, the party girls, the confirmed bachelors, the frat boys, etc. Many of them may be perfectly good people who might very well qualify for the Celestial Kingdom, but they are nevertheless unable to overcome a hurdle of personality that is absolutely crucial to their exaltation; to becoming like God. At the same time, women have an absolutely crucial temporal role in the plan of salvation in providing bodies for God's children, and so we see, that, in order to recover the population lost in the great war of Isaiah 3, the Lord does not kill of the wicked women, but they will, by and large, find a man to reproduce with, via polygamous relationships. The women of Isaiah 4 are more independent than we would normally expect from traditional gender roles. We would normally imagine, all the same though, that they are married to him in the traditional sense, and I have long expected so as well. However, the aforementioned considerations lead me to think that this might not necessarily be the case.
If we consider the concubines of Jacob, I think it falls in line with my above considerations. This is, of course, a different time. I think it is fair to say that Jacob's concubines were not his in any direct sense. They are described as being attached to his wives more than to him. The way it is portrayed, this was likely more a matter of social status than of any inherent flaw in the womens' personalities, so we recoil at what appears to be slavery. It may have been so. It is immaterial to my point. My point is, that they were in a primary relationship with a woman. Not a directly sexual relationship, but it was their primary relationship. They did not sleep with Jacob because of their relationship with him. They slept with Jacob because of their commitment to their mistress. They apparently didn't serve Jacob. It seems apparent that the concubines in these types of relationships did not take orders from the man of the house. He didn't get involved in correcting them either when they failed to live up to their commitments. This was handled by their mistress.
If we go back to my observation that some women and men cannot abide committed relationships with the opposite sex, we see in this model a way in which such a woman could instead form a relationship with another woman which gives her some access to a man by way of her relationship to that other woman. For some women that can only manage stable relationships with other women, this would allow her to reproduce within the context of a committed and stable relationship. (The children of such concubines seemed to have been imputed to their mistresses, so it would seem that if my speculation is somewhat near the mark, then the children born to a concubine would seem to fall under the sealing and covenant which the mistress has with the husband, and I would imagine that this would be established through some kind of covenant relationship the concubine has with the mistress.)
Now, this is just me thinking about the various details we have been given in the context of observations I have made. I do not claim that this is the hidden portion of Section 132, or that what I have suggested is the Lord's law, just that it is the best model I have worked out so far based on the available data. I'm sure it is offensive to many sensibilities, and certainly wasn't needed by the early saints, which is exactly why anything along these lines would likely not be made public. (Again, I am not claiming to have enough confidence in this model that I want to claim I am right. I'm just saying that the offensiveness of it is not a real argument against it. We have to take it as a given that whatever might have been revealed, if there was anything more, was pretty offensive to many sensibilities.)
This would be something akin to a covenant surrogate in some limited sense. In a model such as this, could a concubine later become a wife? Could a widow become a concubine? (There would seem to be less of a point to this, but one could imagine that some widows might prefer having a primary relationship with a good female friend rather than an unsealed marriage to another man, though I might imagine that her sealing to her first husband might preclude such an arrangement since her children are his, and cannot fall under the covenant a potential mistress has with her own husband. That said, a mistress-concubine relationship might not necessarily include that eternal implication, much like a husband-wife relationship does not always include that eternal implication.)