Nope, System Integrity Protection only affects you if you delete/modify system level files. It does not prevent you from creating a `/nix` directory with regula

Nope, System Integrity Protection only affects you if you delete/modify system level files. It does not prevent you from creating a `/nix` directory with regular root privileges, nor does it prevent you deleting it with root privileges. It's only when you try to delete something like /Library, that it then complains. This is one reason why I strongly believe SIP is blown out of proportion. I've used El Capitan since the betas and created root directories, deleted them, added to existing root directories without having to disable SIP. Again, it's only when you try to modify the built in directories inside / does it then complain, and frankly, I am more than happy with that, even with sudo privileges.