We had a discussion in the btrfs mailing list and it was concluded that these changes would deviate from the "default" case [1]. Currently sys admins are setting any subvolume read-only to set the root filesystem read-only. While this is not ideal, this behavior has already been exploited. [1] https://lore.kernel.org/linux-btrfs/20220211164422.GA12643@twin.jikos.cz/T/#t