I hadn't actually thought of that you're right. We still treat they as plural from the perspective of the verb even if we're using it as a singular pronoun.

It really is sort of a hack to use an existing pronoun in a way that sounds least wrong to people.

I wonder if, as a singular "they" becomes more common, we will begin seeing it treated as singular grammatically.

i.e. "They has to make sure their code passes tests before committing it"

It sounds weird after a lifetime of treating they as plural, but is a lot more clear. I have a friend who's S.O. prefers to be referred to as "they", and I constantly find myself confused whether we are talking about his S.O., or some group of people.

I find that hard to believe considering how ubiquitous singular-they is in virtually everyone's speech including yours.

What's bizarre to me is how many people suggest this is some new phenomenon lately when actually it comes so naturally to us that we don't even notice it. You've used and read singular-they probably daily in your life since you could read, yet now you've convinced yourself you're somehow only used to plural-they.

Your post history even shows that you use singular-they which is basically guaranteed for anyone with enough comments on the site: "I assume they [upstream HNer] are referring to Chrome on mobile."

It turns out that context makes this distinction so simple that we totally forget it's a non-issue.

No, we won’t. (Even if singular “they” becomes ubiquitous, which is by no means guaranteed).

You was once exclusively plural. It is now usually singular, but we still use plural verb forms with it (“you are”, etc.). Conversely with on in French, which was once exclusively singular but now means “we” in colloquial speech yet still takes singular verb forms (“on est français” = “we are French”. “il est français” = “he is French”.)

Wow, I never noticed that! I suppose it's rather naive to think that common use would evolve to follow rules, rather than the other way around.

"They have" is already normal grammar for singular they. "Tell each programmer that they have to commit their code."

I really wish people would just invent a new word, rather than breaking our ability to distinguish singular vs plural.

they have invented many... that might be part of the problem

All language is spaghetti code.

German also has Sie playing the role of its formal "you," and the singular "she," in addition to meaning "they." I don't see why it's hard for it to pick up an additional responsibility.