hmm, I have been thinking about this a lot recently - mainly due to time constrictions, once you start dating people other than your (if you have like I do) primary partner, I, at least have found myself dwelling on what would be ideal for me, if I do find this third partner...or mainly saying NO to people who are nice, but I don't feel connected with enough to add as a partner unless they fit some criteria...
I really like the person I am dating now, so ideally that would stick around my life for a yet to be determined future, but if I date a 3rd person (which I would like to do, if it fit into what I was already doing) I would like to date somebody who would become a very close friend to me (aka a chatty communicator who didn't mind talking about their FEELINGS), and who would LOVE to hang out with my husband to kill zombies, and have an independent friendship with him that involved them making plans with each other that didn't need to include me. (Let's say seeing some of these horrible upcoming geeky movies....)
Said err...manly unicorn (in the platonic sense of fulfilling "needs" for an ideal relationship) would also be excited to watch Top Chef or some other horrid reality tv show with me. And find sex a joy. Mainly that last thing, but I admit, the whole bonding over a TV show or other hobby, holds some appeal for me.
After reading some of the other responses, I would say yes, my focus is on the ideal being partners (and metamours) being able to communicate verbally or with the written word, how they feel, what they want, what is going on, or bothering them... so that everybody I am involved with is profiting from the relationships I have a part in, and it's not just about my wants. I don't mind at all "limiting" myself in ways that might make me happy with a partner, if it would cause problems with other relationships they have. Recent experiences have definitely let me know that kindness and consideration by my other partner's partners is much more important than caring about if everything is roses and sunshine in my world.
And on another note, I am pretty damn thrilled how much poly has to offer, no matter that sometimes it offers good, and sometimes bad - I do like the high points!
Happiness will never come to those who fail to appreciate what they already have.