Anne Fadiman, of my generation and fellow sentence-diagrammer, distinguishes the nonbinary they and the generic singular they and makes a persuasive case for both.
My students endorse the singular they not because they’re snowflakes but because they’re activists. The nonbinary they appeals to them because even if they’re not nonbinary themselves, they wish to support those who are; the generic they appeals to them because they wish to be inclusive: Why would you say “If someone has a question, he or she should stand up” when there might be a they in the room?