[mhb]

I would use "he/him" because the convention of using he/him for singular, indeterminate gender is no more difficult to understand than that "they/them" is being used as singular, indeterminate.

Ideally, I would like the people for whom this is important to use a new unambiguous word. Though this ship seems to have sailed despite there apparently being a number of possible candidates.

That aside, the author of the post to which we are referring must know the sex of his dog so why be ambiguous?

[amanaplanacanal]

Language changes. Trying to make it stop is like trying to sweep back the tide. Could go back to old English I guess, or proto-germanic, or proto-indo-European. Or whatever came before that.

And the singular usage of they/them has been going on since at least the 14th century.

[mhb]

I know the argument about its historical usage which isn't a great one if you're also going to argue that language changes. In any case, I'd prefer that it change for the better. An optimist might even hope that it is discussions such as this one which influence how it changes.

Are you suggesting that we dispense with he/his/she/her in all cases? Like in this one to refer to a male or female dog?

[amanaplanacanal]

No, I’m not suggesting that. Languages are gonna do whatever they are gonna do.