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 recovery partition, though it may have avoided some confusion over binaries. Or perhaps that you could mount the /usr partition itself independently if you wanted, assuming primary root was hosed.

Not being able to mount a separate /usr would negate that option.