Not sure i follow - but reproducible in the sense that i want a lockfile (ala Cargo, NPM, etc) for my entire operating system. Allowing me to rebuild it perfectly.

NixOS has a lot of flaws in my mind (though some may just be inexperience), but it has some super solid concepts of configuration first systems.

I have not played with NixOS - my project above was to build a workstation in docker that would hold all my daily stuff at a fixed defined level - like a lockfile I guess but a docker file.

I suspect that even the same docker file has much more wriggle room than a nixos definition - it again not too clear on that