Of course, those are discreet projects that can be picked out when there is a use case for them. Discreet solutions to problems is the hallmark of Unix systems isn't it? Any distro maintainer can choose to enable these if they want, as is the admin.
This is pretty much the whole point of using nix. The system is declarative, so it rebuilds the parts that changed, because all changes are imperitive and atomic. If it didn't rebuild your sshd config and restart the service when you changed the accepted key types, what would even be the point? Coming from a huge ansible background nix feels like ansible on steroids.
FHS incompatibility
Why does this matter? Nix manages all your system binaries and PATHs just like any other distro, so why would it matter where they are kept? Programs like type/which still work exactly the same, and nix imports your dependencies exactly as described in the build scripts when you need to compile something locally.
Its honestly refreshing to see a distro really pushing innovation like this by taking advantage of everything Unix systems are built with and doing something this cool.