I heard this just now on NPR:
As I post this, the audio is not yet available online. Wait for it, though, because it's worth a listen.
Prof. Turley seems confident that, if the Supreme Court defers to the states on the definition of marriage, the way may be open to the eventual legalization of polygamy and - he's quite clear on this point - the many other possible forms of plural family.
At the very least, he thinks, it is possible that "cohabitation" could eventually be decriminalized in Utah, for example, where it is currently a felony.
I don't know that I'm quite as optimistic as he is. Another view of the matter has it that the main reason advocates of same-sex marriage have had so much success winning over the public is that they aspire to the most traditional of institutions, lifelong, monogamous marriage.