News issues tend to work in a sort of priority queue, where only the top three or so get much time in the news cycle. Currently, in American media, the topics are the mid-term elections, Ebola and Islamic State (mixed with conflict in the Middle East in general). Gay marriage just got pushed aside and will probably come back once the election news subsides.

Legally-recognized polyamorous relationships, in one form or another, is probably going to be the next evolution of marriage laws, and there's a bit of discussion about it, but it won't get much attention until it bubbles up to the top of the queue. That might take on the order of years or decades to happen.