I'm not sure what you mean by "a meta build system" vs "a primary build system", but for many years Nix was what our company used to build and package our software. Unfortunately, it was a very bad experience; Nix doesn't strive to be a build system, it strives to be a package manager. The learning curve for writing packages is too steep to expect every engineer to learn it, and when things broke it was often hours and hours debugging into some obscure C library way down the dependency tree that no one in your organization has ever heard of. Worse, very little is documented well or accurately. Trying to figure out, for example, how Nix's python packaging libraries work is frustrating--partly because there is no obvious way to find the defining file for a given package dependency and partly because the package definitions in nixpkgs are rarely documented. These are all tractable problems, but Nix doesn't (seem to) aspire to solve them.