I'm sympathetic to what you're saying but there's a part I just can't get on board with at all. I don't know if it's just that I come from a really different society to your one or what is going on here, but this paragraph doesn't ring true to me at all:

it’s never been socially acceptable to use they/them for a known person of a binary gender, and I’d argue that it’s even less acceptable now, thanks to the common adoption of they/them as a personal pronoun for known persons of nonbinary gender.

It's totally socially acceptable where I am to call people "they", or at least it always has been.

Didn't mean to insinuate anything about your English btw; in my experience most native English speakers don't have much interest in historical useage or etymology. Formal English style guides have only come on board with singular "they" in the last 15-20 years despite everyone using it colloquially for decades and decades.