These aren't really used at all in real-world English though (at least American English). So the result would be a very awkward phrase and probably a phrase that is understood by fewer people than before.

The technically grammatically-incorrect plural pronouns come off sounding better and in my opinion are the better choice if the use of gender-specific pronouns is an issue that needs to be addressed.

I don't personally mind the use of masculine pronouns to indicate a generic person, because I think there's nothing inherently wrong with it, but in the tech world it's good to be careful as there clearly are gender issues to be sensitive of. I think another good solution to this kind of wording issue is to just use masculine pronouns in some places and feminine pronouns in others.

Using obscure and/or not generally understood words when other more common and perfectly valid words exist in common speech is hostile to anyone who isn't a native English speaker. And many that are.

Using those invented words is 'hostile' to more people than any other option.

If the pull request had used one of these I could understand the request being closed, one, they, and them sound much more natural.