That is the opposite of my understanding of the history here; my understanding is that "they" has, for most of the history of written english, been used a gender-neutral singular pronoun, and that it was a prescriptivist movement in the late 1800s that attempted to away with that practice.
The gender neutral singular "they" has a long history, is correct, and should be uncontroversial.
You misread me. The effort to eradicate singular "they" is a late 1800's movement, and, I agree, that movement is archaic. The singular "they" has been a feature of English since Chaucer and remains current; Conrad used it, as did CS Lewis.
The gender neutral singular "they" has a long history, is correct, and should be uncontroversial.