I see a major issue with reserving singular they for "writing in the context of gender diversity." Let's say I want to use singular they in the context of discussing a doctor because I don't know if I'm going to see a man or a woman, or a transgender man or transgender woman, but I know that I'm only going to see one person. If I say "he or she," I'm imposing the gender binary. Do you believe there is a gender binary? The APA does not believe there is a gender binary (https://www.apa.org/practice/guidelines/transgender.pdf). And if I write "he or she" I'm also implying that there are no transgender doctors. Are there no transgender doctors? If there are, then in discussing which doctor I might see, I'm discussing doctors "in the context of gender diversity." Any discussion of people implies a discussion of gender diversity, unless there is no gender diversity, but the APA does not believe that (https://www.apa.org/practice/guidelines/transgender.pdf). I really think you need to get on top of this before gender and trans* activists take this up as a cause. I believe the APA doesn't have that good a record on gender and sexual orientation (http://behaviorismandmentalhealth.com/2011/10/08/homosexuality-the-mental-illness-that-went-away/). For example, I cannot say "Every student at Blank University needs to turn in his or her paperwork to declare an individual concentration" (where "Blank University" is the name of my school) because I know that we have transgender students and I work with them. Saying "his or her" imposes the gender binary. I understand rewriting the sentence to avoid singular they, so please don't bring that up--I just can't think of a good example of a necessary singular at the moment.