Being able to roll back changes to the OS sounds great.
I don't know a ton about NixOS, but rolling back changes is getting more and more common. openSUSE distros enable snapper by default (btrfs snapshots and rollbacks), and you can get the same working w/ pretty much any distro, provided you use an FS that supports snapshots.
I'm currently testing out openSUSE Aeon (very similar to Fedora's Silverblue, Steam OS, or Bazzite), which has an immutable base and relies on flatpaks for all applications. So far it's working pretty well, and it's an interesting concept:
- rolling base - always latest kernel and desktop environment, and you don't need to worry about it
- containerized applications - the version of each app doesn't depend on the base os
Maybe you'd like something similar?