Do polies want to marry each other or do such relationships not lend themselves to permanence above a threshold of partners?

I personally know one three-person poly family that consider themselves married and would be legally married if they had the option. I know of others as well.

Some changes would need to happen for poly families to get the same rights as married couples, particularly when it comes to taxes. And I assume that some hub-bub would be created about sanctity, and people getting married "just for tax reasons," and I am sure someone would reference cults trying to get tax exempt status even though it is something entirely different. I would even expect backlash from the gay community, who would be trying to make it seem like gay>poly wasn't the "slippery slope" that anti-gay marriage activists now claim gay marriage will lead to.

Frankly, it's probably easier to just try to form a non-profit group that acts like a marriage arrangement if one wants the legal benefits of marriage, with all personal assets of members going to the company before being redistributed to the members of the unit, although I haven't personally tried this.

Given the dug-in fight over gay marriage, the poly families I know aren't holding their breath. Most have just accepted that their fight probably won't even happen in this generation. As to whether or not it should happen... well, I doubt there will be any hideous consequences from allowing polyamorous unions to be recognized by the law, outside of the people shouting about it.