I’m polyamorous and part of a network of poly people. (That tends to happen: your girlfriends each have other boyfriends who have other girlfriends, you get daisy-chain connections leading out in various directions). I know some people would like the protections and status afforded by marriage. Me, I’m disdainfully wrinkling my nose at the institution of marriage and feeling no interest or attraction. Opinions vary.
Frankly I’d like to see legal flexibility in setting up households and partnerships. Unlike gay people, who quite reasonably felt second-class-citizenned by the notion that domestic partnership oughta be good enough for them and marriage enshrined for hetero couples, I don’t feel like the legal arrangement need to be marriage or in any way based on marriage. But it would be nice to be able to formalize some things without having to incorporate as if we were going into business or something.