That's a really compelling workflow. On the Linux side I've heard of openSUSE's MicroOS doing something conceptually similar with BTRFS snapshots and atomic transactional updates, though I haven't actually run it. Different mechanism but it sounds like the same instinct. Never let the running system get into an inconsistent state during an upgrade. The "boot just once" plus jail-the-clone-to-upgrade combo you described sounds genuinely clever, hadn't realised the bectl integration was that smooth. Void Linux is just a name to me at this point, might be time to actually look it up.