afaik btrfs is can do all the things you listed.
im using open suse with btrfs and can only recommend it.
the setup was easy ( asside from non btrfs related issues with the finicky installation media)
and open suse automaticly sets up subvolumes and snapshots before and after each update
to take advantage of btrfs
id doubt it will be nearly as bad unless they try to screw it up on purpose
it was already a far better experience even before the steamdeck released.
the only thing that im currently missing is support for mods (i.e. nexus mod launcher) and id doubt the target audience of a “steam console” would be bothered that