NixOS kind of extends the idea of reproducible builds. Any snapshot could be a guarantee that things just work. This can also be extended onto the user base - if one user has solved a problem, it should be solved for all of them. So we can jump from guarantee to guarantee here.

My only gripe with NixOS is Nix. I think that this is also the biggest drawback of NixOS. I don't have an alternative; but perhaps it may be better to allow any format to be used, rather than force nix onto everyone.

Another issue is that, for a reason I don't quite understand, a few years ago NixOS' quality appears to have gone down, e. g. nobody cares about documentation anymore. This is probably not a huge obstacle per se, but I did not feel I should invest that much into nix (which I dislike) when the documentation leaves a lot to be desired. Ironically this also means that the whole idea behind NixOS, falls flat, if the documentation is poor. They really should make the same guarantees for their documentation, just as they do for the software ecosystem too.

Nobody cares about documentation anymore though - AI has won. Just try finding high quality documentation via google search; it is slop world now.