If you lack the majority, you have fewer options, most of which devolve to coups and forcing an ouster.
I don’t know how to read this letter in any other light.
I think it may also be symptomatic of the peculiarly leftist failure of assuming the inevitability and reasonableness of their positions as universal and that to disagree makes one a priori a bad actor.
Forking Nix would take an immense amount of effort, and the maintainers are already overworked. There would absolutely be a community split, which means that there would be even more work required than before to just maintain both of the forks and keeping them in sync. The nix language itself has no spec right now, meaning the behavior is defined by the singular existing implementation. Forking Nix itself will very likely introduce incompatibilities that are impossible to remedy. A lot of the power of nix comes from nixpkgs (where the entirety of NixOS is maintained as well), its build system hydra and the binary cache, the servers, CDNs and agents for which are sponsored by external companies (we're talking 0€ cost for something that would normally cost 10s of thousands every year). Forking would lose all of that, it's pretty much impossible financially.