Here's a very nice case of modern sex-neutral pronoun-choice style, with the unusual feature that the antecedent for the two occurrences of singular they (which prescriptivsts hate so much) is not only a definite noun phrase, but a definite noun phrase denoting a unique individual. The sentence comes from a Buzzfeed listicle drawn from "Shit Academics Say" (@AcademicsSay) on Twitter. I underline the antecedent and the two pronouns:
We wish to thank Reviewer 2 for their critical feedback & sincerely apologize for not having written the manuscript they would have written.
The special feature here is that the people writing are not permitted to know the identity or the gender of the person denoted by the phrase. Academics submitting to a refereed journal never know who their anonymous reviewers were; all these authors know is that Reviewer 2 hated their paper and wanted them to write a different one. They have no way to know if the reviewer is a he or a she. And especially in the terse Twitter medium, saying "for his or her critical feedback" and "the manuscript he or she would have written" would be much too cumbersome.
See this post for another remarkable case, where a unique but unidentifed person is referred to by a singular they, and in fact the sex of the person is known as well.