They instead of 'him/her'?

If it’s good enough for Walt Whitman (“I contain multitudes”) it’s good enough for me.

That’s the way the English language I grew up with does it. The rest of y’all are finally catching up with the South, linguistically.

Great idea!

My problem with “they” is usually not with ambiguity of gender, but with ambiguity of quantity, whenever the gender is implied, such as in: “Spoke with John and they decided not to buy the house”. Now of course one could use “both of them”, but what if only John decided so ? Should I talk to the John’s partner as well ?

There’s no such thing as formal acceptance by grammarians.

But in addition to the other citations, the Wikipedia article discusses historical precedent.

Goes along with the equally regional “we is doin’ good!” or “They is a-comin’ tomorrah!” and “I be happy”? Channeling Jed Clampett?

I’m fairly certain this is a bit out of date now, but when I was a kid, some of my family who lived seriously far out in the boonies would distinguish between “We all” and “We uns is”. The first was First Person Inclusive, while the secon was First Person Exclusive:

FPI: We all are going into town. (I’m telling you that we, including you, are headed for town.)

FPE: We uns is headed into town. (I’m telling you that a number of us, not including you, are headed for town.)

I’m rereading My Ántonia and the title character is called Tony throughout.

Depends on what you mean by grammarians. General purpose dictionaries, such as Merriam-Webster, are all descriptivist. Style guides tend to be highly prescriptivist.

So we have M-W being fine with the singular they because that’s how people use it. And we have Chicago still considering it to be non-standard:

They don’t seem to have changed their view much for the 17th edition (cite), but I think they’re coming around. I don’t have a copy handy, but I believe that the 17th suggests that formal writers “be wary” of using the singular they. Maybe for the 18th.

They coexisted as singular pronouns on the way from being a plural/singular pair.

As far back as the 14th century, the plural forms ye and you began to be used to address one person—usually a superior—as a mark of deference and respect. This change could have been influenced by the first-person plural we (the royal “we”) used by sovereigns or reflected the impact of French politeness at work in Middle English.
You Definition & Meaning - Merriam-Webster

Norwegian by the way still uses the second person plural this way, although it’s gone from “everyday polite” in the 1960s to “speaking to royalty and people who were already very old in the 60s” today.