Thought the article was great overall. I would nitpick the jumping off point a bit though.
The polls appear to have been wrong by around 2-2.5 points. That's actually closer than they were in the last election, and is a very typical amount of error. To ask polls to be any more accurate than this is a very tall order, and polls accurate to within 2-3 points are still extremely useful.
If someone thought this election was a lock then the error was looking at the wrong sources. It was not a failure of the system to make a reasonable prediction. 538 and the betting markets had Trump's chances in the 20-30% range. Elections don't have to get very lopsided at all to end up 90%-100% in favor of one candidate. Both sources deemed Hillary the favorite, but also clearly categorized the election as too close to call.
Point. The polls were not hugely off.
The felt sense (which I had) that Trump was a 'crazy, impossible' candidate and so wouldn't really win, was off.
Factual data is useful, and even biased data (e.g. polls, government-published statistics, scientific papers) are useful, and the fact that polls & Nate Silver were not hugely wrong is evidence that we don't have to throw them out entirely.
What's scarily non-useful is opinion.
Upvoted. I'm not sure how to phrase this without sounding sycophantic, but here is an attempt: Sarah's blog posts and comments were always top quality, but the last couple of posts seem like the beginning of something important, almost comparable to when Scott moved from squid314 to Slatestarcodex.