A phrase I keep coming back to that sums up the "taking out the ego" and "non-hierarchical" element: "The people in the relationship are always more important than the relationship itself." - In other words, the relationship is here to serve us, not the other way around.
This perspective helped me a lot because I had been in a possessive monogamous relationship and raised in a traditional religious home. I always felt I had to make the relationship work or I was somehow failing, and that kept me in unhelpful situations.
I've really enjoyed "Sex at Dawn" for historical context and "More Than Two" as sort of a Bible for navigating the undefined territories. Also this old book "Open Marriage" I randomly found was surprisingly helpful. All resonating with what you're saying. Great article!