I'm not sure what the takeaway here is, that people who make a decent income should be barred from marrying other people who make a decent income? I usually like Edsall's analyses, but he seems to be mixing correlation and causation a bit. One of the few things I agree with conservatives on is that the disintegration of families has had a hugely negative impact on society. I also don't think that people should be criticized for maintaining a two income nuclear family, as if it's an option only available to high earners.
It's an essay trying to say too much so it ends up explaining too little. He's rolling with the tried-and-true "vanishing middle class" trope and adding on a "democrats are republicans, republicans are democrats" trope. Which, really, explains why Bernie Sanders is losing the war of attrition - the "other fifth" likes Clinton's finance policies. That whole "pulling away" thing ties in with another New York Times argument that pisses off the rest of the country: Six figures is not enough.
If anything, he's basically saying "elitism is real" which is kind of the NYT's masthead at this point.