Earlier quoted context omitted.
mtab is not a problem anymore. On Arch, /etc/mtab is just a symlink to /proc/self/mounts. As for the recovery partition, you don't need the split for that, either. Just have a live system on the recovery partition that mounts the normal root FS. Then you can chroot into there for recovery tasks.
Right, that seemed to be the mtab solution Debian were angling toward. I think there were some odd edge cases where it didn't behave well, though I don't recall what those were. Perhaps the ability to specifically edit the contents to allow fixing of fubared mounts -- almost certainly loopback or NFS, both of which get quite twitchy at times. I don't recall my precise thinking on a clean root vs. /usr split on the re…
You can mount the root to e.g. /mnt and symlink (or bind-mount) /mnt/usr to /usr, if that's what you need.