Allowing behaviours to add structure to the site admin

I’m looking at migrating a fairly substantial back-catalogue of articles
and other content into radiant, and the handling of articles under the
archive behaviour looks to get pretty unwieldy once you’ve got a
couple-hundred articles there.

I’m proposing adding a way to allow behaviours to modify the structure
of their children as displayed on the administration tree. Attached is a
fairly hacky implementation of this (diff against current svn - revision
56). I only started poking around the codebase a couple of hours ago, so
go gentle on me.

This would also be useful for a second behaviour I plan to add to
separate child pages alphabetically.

Does anybody else see the value in pushing forward with this?