Maggie Gallagher has a post up on IMAPP about the NY Times' recent love affair with polygamy. The article she references is from the Arts section and consists of showing several women from real polygamous relationships in Utah the first episode of Big Love (the new HBO series about your friendly neighborhood polygamists) and getting their reaction to it. (They think, among other things, that it focuses too much on sex and not enough on the importance of religion in the polygamous lifestyle.)
Maggie's point is an interesting one: For many intellectuals, the next logical step in any given progression is always a point of intense interest. Thus, the NY Times elites, having some time ago settled on the idea that many 'non standard family' configurations such as gay marriage make sense, now find it intriguing that polygamy may also be a viable lifestyle. This doesn't necessarily mean that they are actually in favor of polygamy. (And the Mormon fundamentalist polygamists they're interviewing probably aren't in favor of many of the cultural innovations that NY elites support.) But they do find the idea that polygamy might be another valid lifestyle interesting.
However, cultural standards are essentially that set of standards which no one thinks it makes sense to question. In 1900, there was a cultural standard against unwed motherhood because almost no one was willing to even imagine it as a moral or cultural option. By the '60s and '70s, voluntary single motherhood was becoming imaginable, even though most people tried very hard to avoid it. However, a generation after it became imaginable, it now isn't considered all that surprising for a woman to intentionally have a child out of wedlock.
Gay marriage as a lifestyle first become imaginable in the '80s. Much before that, not only was it not imagined by the culture as a whole, but so far as one can tell it wasn't even particularly desired by active homosexuals themselves, who celebrated their freedom from straight relationship standards.
Now the idea of polygamous or multi-tiered family relationships seems intriguing to some cultural elites. And without any generally accepted cultural standards of what a marriage or family is at an essential level (other than 'a relationship of people who love each other') there is no reason why the idea of 'multi-marriage' might not also become unsurprising in certain segments of society.
Which goes to show, you need to be careful what ideas you play with.