Thanks for the link, Sparklybutold. I was also curious about the claim that neopronouns have been in popular use for centuries. "Neopronoun" refers to (at least) two distinctly different things. I've mainly heard it used for self-assigned individual personal pronouns (e.g., I ask you to refer to me, specifically, as "per" or "fae" or "frog"). But apparently it can also refer to a new or repurposed word meant to be used universally instead of the standard third person singular personal pronouns (he, she, it, and arguably they). The article only deals with the second case.
If your colleague is asking that EVERYONE be referred to as per, then I agree there's precedent. But if your colleague is requesting to be referred to as per as a personal, individual exception while continuing to use and accept he, she, and they as the default for others who haven't also requested an exception, I don't see an historical precedent.
The example the author gives of "thon" as a contraction of "that one" is still a universal pronoun. It does refer to a specific person in the context of the conversation, just as he or she would, but the word "thon" is not specific to that person. Someone who says "I met thon in the park" where "thon" stands in for "my neighbour John Smith" would likely also use "thon" to refer to John's brother Sam Smith if Sam were the person being discussed instead of John. It's not specific to John, nor requested by John as a personal exception.
The other examples in the article are personal pronouns set up for everyone or for a particular group of people, not by request for a specific individual. They're either attempts to create a universal sex-neutral third person pronoun ("it" has negative connotations as it is often assumed to be reserved for inanimate objects, thus seen as dehumanising) or to refer to an alien race, e.g. in science fiction, who do not have sex characteristics as we know them. But these terms would be used for everyone who fit that description, without the individual having to ask.
Many languages use non-sex-specific personal pronouns by default. For example, in Hungarian the same word is used for he, she, and it. Person/per/pers/perself was used by Marge Piercy in Woman on the Edge of Time (1976) as the "standard" personal pronoun for all people, replacing both he and she in a fictional future society where men and women were equal. Everyone was referred to this way, including people from outside of that society (e.g. Connie, a time traveller from the 1970s). To leave the linguistic sex binary intact but have an individual person request to be described by a separate non-sex-specific term would have defeated the egalitarian/nonsexist purpose - it draws attention to and reinforces the binary, rather than erasing it.