It's not that easy to change the default store dir.
https://cache.nixos.org/nix-cache-info has it hard-coded to /nix/store. If you want another one you'll need a whole new cache. But Hydra only works with one cache, so now you're deploying a second Hydra build farm.
One of the cool features of Nix is that you can evaluate some nix code on macOS even if the target build host is Linux. And then ship the .drv over to the build host. But that only works if both hosts share the same store dir.
So now you're looking at moving the whole community to use /opt/nix. And thinking of how to upgrade the existing users to it.
And fix all of the tooling we built that assumes /nix/store as the store dir.
So far nobody had the courage to tackle this huge task.
https://cache.nixos.org/nix-cache-info has it hard-coded to /nix/store. If you want another one you'll need a whole new cache. But Hydra only works with one cache, so now you're deploying a second Hydra build farm.
One of the cool features of Nix is that you can evaluate some nix code on macOS even if the target build host is Linux. And then ship the .drv over to the build host. But that only works if both hosts share the same store dir.
So now you're looking at moving the whole community to use /opt/nix. And thinking of how to upgrade the existing users to it. And fix all of the tooling we built that assumes /nix/store as the store dir.
So far nobody had the courage to tackle this huge task.