I consider interracial in it's adolescence. About five to ten years ago, it was in it's youth - just common enough to be considered a bit rebellions. Now it's in its adolescence. Mainstream media has picked up on the trend (like they did with homosexuality) and it's being introduced in commercials, TV shows and movies, not as taboo, but more along the line as accepted. In a few years, it will become, like I said earlier, so accepted that it won't be noticed.
Open marriages is the next hurdle I think. Once the IR aspects become mainstream, then the next thing to unfold will be open relationships. Either that or non-marriages. By that I mean that people will live together for extended amounts of time, possibly coming and going, or perhaps more introducing others into the dynamic.
Remember, communes were tried in the 60s, but folks (society in general) pretty much failed to accept it. Your first clue (in my opinion) will be when it starts coming up in television shows. First you'll see the woman with two partners. After that's accepted, it will be the male with two female partners. The male (again, in my opinion) will be slower to develop because it's too much like what the Mormons preached, but I think that a woman with two males will help establish the female-superior dynamic which society will feel easier to accept, as she isn't the one being 'prayed upon' but in the controlling roll.
Something I think society will be quicker to accept.