I've looked at a lot of other immutable distros and I might just end up using one of those, but I feel like taking on a bit of a challenge and there's a few things I'm not very keen on with existing solutions (last paragraph is my idea if you want to skip the context).
Most immutable systems I've seen require a reboot in order to apply system changes. What is this, Windows? Yeah, reboots are quick but restoring my windows and getting back into my groove is not quick. Also, every immutable OS I've seen wants you to opt-in to a rollback. Rarely do I see the full effects of installing a package or altering a config immediately. By the time I notice an issue maybe it's too late to rollback to before the change or maybe I've done a few other things since and I don't want to rollback everything. I would much prefer to make "rolling forward" or persisting changes to be a very conscious process.
I started messing with BTRFS and I think I've come up with a process that will get me what I want, no matter the distro. Please poke holes in my idea. So I think I can use BTRFS to hold data for the rootfs in three different subvolumes (at minimum): root-A, root-B, root-Z. root-Z is my golden image and it represents what I want root to look like after reboot. root-A and root-B are the active and passive instances of rootfs, but which one is active will flip-flop after every reboot. So if I boot with A, B gets replaced with the contents of Z. In the meantime I can do whatever I want with A. Not sure how I'll update Z (chroot or "promote" the active subvol to be Z) but without an update every reboot is an automatic rollback.
Thoughts?
IIRC main Fedora used to not do this until some update crashed people's sessions including the update process which left their install in an unbootable state.
The ostree based versions like Silverblue avoid this by their updates not touching the running system and instead creating a new folder structure with the updates applied that will be booted into on next boot.