> I feel like Nix lacks a clear vision of its future.
There's various high-level plans that I think have a decent consensus, but not enough people have authority to make things happen. This means that more interesting PRs often rot.
> focuses on desktop systems
Nobody actually prioritizes desktops over servers, and the core design is quite agnostic, but because Nix is over a decade old, lots of old code and documentation do make it seem this way.
> yet apart from Linux no other server systems are officially supported
Other unices work do for userland Nix, and darwin has official binaries which would be the moral equivalent of official support. Also check out https://github.com/triton/triton a fork of nixpkgs which aims to have a NixOS work with FreeBSD kernel, and https://github.com/cleverca22/not-os to better make immutable OS images.
Please don't say things if you don't know about them.
Just to prove my point, we've recently merged a branch for hardened compiler flags. This is mainly for server security.