but it just isn't part of the cis comp het system

Absolutely agree and the middle class thing isn't wrong. Though funny enough before it became more mainstream known many places in which good munches and workshops in my city happened (often under labels somewhat different to polyamory) they were from leftists, sometimes feminist, sometimes autonomous somewhat anarchist groups. So your point about a feminist polyamory which is an alternative to both the official and inofficial polygamy (think Elon Musk or Donald Trump) as well as the patriarchial polyamory which is exclusionary in terms of gender identities in practice does really vibe with me.

it just isn't part of the cis comp het system

Absolutely.

There would of course be challenges brought in in addition to other points that poly means exclusion of neurodivergent people, not only due to sane-ism, but due to the non materialist idea that enough communication and talking about problems does fix them as example.