FWIW that sounds pretty much like mkinitrd on openSUSE. A directory structure
in /lib/mkinitrd/ containing startup scripts that may be put there by installed packages
(e.g. /lib/mkinitrd/scripts/boot-lvm2.sh is owned by the lvm2 package). Adding busybox
is just adding "busybox" to the feature list parameter of the mkinitrd call. The scripts
(including mkinitrd) are commented (which already saved me once) and the mkinitrd
manpage even contains instructions how to mount the root partition from a rescue
system with necessary bind mounts to be able to execute mkinitrd.
Seems like such a structure is the result of natural evolution :)