My point is that the lack of boot flexibility caused a lot of problems. If we want to be able to rely on people to get the job done even on days when something is wonky in the bits, then we should give them boot flexibility. NixOS just happens to do it especially well.

As for ZFS... Dealing in filesystem snapshots is comparatively a bit awkward. If you want to recreate that config elsewhere you have to move the whole snapshot rather than just the recipe for building it, and even then it'll break if the system architecture is different on the target machine. If you've got two of them (perhaps labeled "good" and "bad"), you're not going to get anything friendly when you try to diff them, nor is there an obvious way to use things like `git bisect` to reason about where the problem occurred.

None of these things are show stoppers, but working with code that defines some state is just so much easier than anything you get out of a filesystem which happens to remember that state, but can't tell you why it should be the way it is.

> As for ZFS... Dealing in filesystem snapshots is comparatively a bit awkward. If you want to recreate that config elsewhere you have to move the whole snapshot rather than just the recipe for building it

That wasn't the highlight of the point. It was that you can restore to a known good version of the operating system, effortlessly, regardless of what the operating system is. It could be Ubuntu, Nix, or FreeBSD. Broken OS, select an older snapshot in the boot loader, and you're golden again.

I think that IT departments are going to disallow their users that kind of freedom unless they have more information/control about just which configs their users are allowed to boot to. It has to be more descriptive/composable than a pile of bits and a timestamp or they won't go for it at all.

As much as I want to put all the power in the hands of the user, I'm sympathetic to the plight of the IT guy who has a team that always boots to "last known good" config thats several years old because they just don't trust updates in general.