Wow, an interesting thread.
I guess no bona fide unicorns have joined in yet? My reasons to go couple-hunting:
1) I already have a primary I'm not sexual with.
2) I'm not interested in having biological children, but would be very supportive if the couple did. I would cherish a co-mother/auntie position.
3) Bisexuality is a strong factor.
4) I love the energy couples have. It would bring me deep joy and contentment to see to people I love love each other.
5) I have a very high need of physical and emotional space.
I know that point 1) already disqualifies me from true unicornism, and I'd never agree on a polyfi triad. But that might just be general need of space - I'm not the least bit more interested in bigamy than I am in monogamy.
Me: bi female in my twenties