That said all of the legal agreements become far more complicated and likely null and void if one person drops out or is added. I think an argument could be made, but with the complication you're basically saying polymarriages would be like corporations, with their associated complexity.
Polygamy as practiced now is a "bring more childbearing women" into the flock type thing, which is by nature non-equitable. I doubt most folks in a polygamous marriage (by choice) would want to get involved in a polyamorous marriage and as such, I think you can't legally support a non-equal union of that sort.
Hmmm, please excuse my ignorance in such matters. I only married one woman and that is quite enough.
>you're basically saying polymarriages would be like corporations
Yes, exactly. Well put.
>with their associated complexity
I can't even begin to imagine the complexity, legal or relational. However, I can imagine situations where such an arrangement could be beneficial to the individuals involved.
Quite literally, I imagine it would go something like:
Do you take this woman to be your wife? I do.
Do you take this woman to be your husband's second wife? I do.
Do you take this man and woman to be your husband and second wife? I do.
That's how three adults could all consent.
You can argue that someone is being forced to say yes, but you could argue that in any type of marriage or contract.