In terms of hierarchy, I'll say the same thing I have said on other threads today: I think that a polyamorous relationship is the ability to have more than one romantic and/or sexual relationship without fixed limitations on how emotionally entangled any of those relationships can become. In a polyamorous relationship, hierarchical terms like "primary" and "secondary" should only consistently indicate the level of practical entanglement you have with the person concerned. Ie. your spouse who you share a home, children, financial obligations, family commitments etc is your primary partner and your girl/boyfriend who you see a few times a week, have no or few practical entanglements with and may or may not also have a primary style relationship is your secondary partner.
The minute your secondary partner is defined as "the person I have to love less, I believe you are moving into a different realm of ethical non monogamy and heading towards an "open relationship".
Generally, I am a fan of quite precise labels; as well as being on the autistic spectrum and preferring things to be quite fixed, I genuinely believe that if we use these labels in a more defined fashion, people will have less incidences of misunderstandings. If you approach someone who says they have an open marriage, you will automatically know that any potential relationship you have with them has quite a definite ceiling in terms of how emotionally/romantically attached you can become. Of course, there will always be a scale within a scale and you will only find if you are on the same place in that scale by communicating. But at least it will give all people looking for non monogamous relationships a concise way to indicate their limitations before there is any emotional attachment and thus the possibility of a misunderstanding and people getting hurt.