I really wanted to move a load of things like default settings and init scripts out of /etc so that you could have a complete separation between system things (which can be on a read-only filesystem, support A/B upgrades, and so on) and user-modifiable things. MacOS has done this now and it's great. Updates are just 'download this disk image, extract it to a new volume, set the new volume as the boot one, reboot, delete the old one'.

You can get pretty close to this with ZFS (I'd love for upgrades to be possible with zfs receive!) but with other filesystems you have a problem with fstab. If /etc is not part of the root image, you need to be able to find it somehow.