I think monogamy+ can work for a lot of people if they put in the work to manage their insecurities and deprogram from societal messages that support jealousy and the idea of ownership of each other. Pair bonding is an ancient dynamic, but until fairly recently, it didn't necessarily involve strict monogamy - and in many cultures it still doesn't.

Most Americans are kind of rabid about the "rightness" of monogamy even though a huge number of them also engage in infidelity of some sort. Making any sort of non-monogamy work takes a lot of communication and a lot of being responsible for yourself - something that not everyone wants to bother with - but then they end up with bad results. I don't think most relationships are ready for full-on polyamory but some form of monogamy+ could work for a lot of people if they would embrace it.