Someone queried the Associated Press Stylebook to find out whether AP has accepted their as a gender-neutral singular pronoun, to which the editors of the stylebook replied no. Testy Copy Editors commented on Facebook: “AP holds the line, for now, against the idiot epicene.” 

I know any number of editors who share this visceral dislike of the singular they. It cuts no ice with them that linguists have demonstrated widespread use by reputable writers for centuries (an extensive set of links here, for those receptive to evidence), or that we somehow contrive to use you in both singular and plural senses without growing red-faced and shouting.

Neither are they likely to be impressed by my own anecdotal evidence, that in the year or so that I’ve been allowing singular they into print at The Baltimore Sun, not a single reader has registered a complaint at these violations of the purity of English. And neither have the AP Stylebook editors responded to my repeated prodding on the issue.

One sees a familiar circularity here. The stylebook editors insist that their rulings follow the way the language is written, and many of the written sources they consult have gone through the hands of editors following the AP Stylebook.

Jonathon Owen, in his master’s thesis at Brigham Young, “At the Coal-Face of Standardization: Uncovering the Role of Copy Editors in Standardizing the English Language,” argues that “educated written usage and edited usage are not necessarily the same and should not be conflated,” because copy editors routinely alter texts to reflect stylebook preferences, whether those preferences are warranted or not.  
Another way to say this is that copy editors have been keeping AP style rules on life support. It will be interesting to see, now that publications have drastically reduced copy editing, or eliminated it outright, whether corpus data will continue to disproportionately reflect edited usage over educated written usage.

Bryan Garner advises avoiding noun-pronoun disagreement wherever possible, because if you use singular they, “some people may doubt your literacy,” which falls considerably short of his declaring the usage wrong. In the same  CONCORD entry in Garner’s Modern American Usage, he explains: Why is this usage becoming so common? It is the most convenient solution to the single biggest problem in sexist language—the generic masculine pronoun.”

So it was, so it is, and so it will continue to be, until even the AP Stylebook can no longer pretend that it is an error and not standard English.