> Your objections seem to be based on not understanding the Nix package manager.
The objection is NOT that nix will somehow screw up the system by having conflicting packages. I'm objecting to the concept of user-installable packages, under the assumption that the package manager handles conflicts perfectly.
There are various objections (5 have been listed) the one closest to what you describe is that someone installs X to build Y. Initially this is fine because Y is a non-critical internal only application and a stop-gap measure until the real solution can be released. Of course Y morphs into something more and becomes a critical permanent external application and needs to be brought into compliance (moved to a secure server, audited, etc), and the approved systems are not capable of running the required X.