I'm always wary of definitions for things that require complex explanations, and are subject to debate. That doesn't mean it's invalid, but it just speaks to - and I hate to say this - a possible influence of academic studies or literature or class content.

I once asked a person who described themselves as 'ethically non-monogamous' what that meant, if it were possible to love more than one person. I was told I was presumptuous, I needed to do more reading, and she gave me multiple paragraphs that interspersed terms like 'the traditional family model' that suggested this was coming from literature.

So - unpopular opinion, and an alternative to "the world is reverting back to the original state of our ancestors with polyamory and hypergamy" -- what if a lot of these definitions are lifestyles that are catching on, due to certain personality proclivities that have always existed, and by making complex explanations we've given them acknowledgment?

In other words, niche lifestyles that have been very much studied and many academic essays written.