Seems like an author that doesn't understand the spirit of FOSS. The nixos team was clearly allowed to use it and include it when asking for some technical merits as to why, and even offering many alternative options to appease the author the author seemed to just childishly stamp their feet and say, "because I said so". Eventually the author took the position of "taking my ball and going home". Why is a person like…
I get being done with something when you've had a bad experience, but the maintainers here went to every effort to accommodate, and did so in a friendly way.
It reads like this guy wanted a fight and an excuse.
I think the correct answer is to just make the fork as proposed and use that instead, it solves the problem and removes the guy from the equation entirely. The fact he rejected it doesn't matter and he can be angry all he wants.