I also found it humorous/ironic that for something that is all about like... deterministic and reproducible or whatever: https://github.com/NixOS/nix/issues/458#issuecomment-1019743... it touched the system in a bunch of places and was a zoo to uninstall
Some of this, though:
> touched the system in a bunch of places
is probably unavoidable. For a daemon to persist, you have to plug into launchd. To get a writable /nix, you need a special volume. To plug into all the shell environments and set appropriate environment variables, you need to configure a bunch of shells.
Some of that can be improved, for sure. Some of the logic for setting Nix profiles could be moved out of shell scripts, and then only a few static environment variables could be set in /etc/environment instead of modifying shell startup configurations to source a special script, for example. But the messiest part of a tool like Nix is always going to be where it plugs into some other system which has none of Nix's guarantees and isn't under Nix's control.
An improved installer (maybe just like the one in the OP! I haven't tried it yet) is probably the best that can be done here, in automating the handling of those messy points of integration. But it will be a matter of hammering out bugs over time like for any old installer, rather than something that relies on the kinds of guarantees Nix tries to make for its own internal operations. An uninstaller for Nix is something that can (and should!) be done well, but not by simply relying on Nix's usual guide rails.
On Linux there are far few steps: - delete /nix - delete build users (could be removed in the future) - delete she'll script files in /etc/profile - delete systemd nix-daemon service - delete symlinks in user directory