The singular "they" has been around since Shakespeare. It's not a new idea, but rather, we're going back to old ideas. Like the time when language was fluid and a game that writers played to entertain and teach.
Now the Prose Part
If you want to demean a male character, you say things like, "He ran like a girl." If you want to insult a female character, you say, "She looked man-ish."
But what if we took away these stereotypical insults? What if we left the old world behind?