Ideal Wordpress Plugin

For various reasons, I've a WordPress plugin in mind (but not the skill to create it). I wonder, is anyone out there able to do this? The Task: Editorial Control

The Job:

A user would be restricted to maintaining posts within certain categories (and subcategories). Ideally, they may have several such categories. (E.g. if a site has categories A and B, with subcats Aa, Ab and Ba, Bb, the user might be allowed to post in A (and subcats Aa, Ab) or in Bb (but not B)).

A user would be restricted to making pages with a particular ancestor (e.g. a user can make pages with X as a parent)

Users would be 'groupable' (i.e. groups of similar users could be created).

The roles of 'editor' and 'publisher' within those sections would hold. Publishers would be alerted of anything the editor submitted (so content wasn't missed).

Group permissions would apply (so that I could define a group of people able to edit page X and create subpages).

Is this clear?

Does this plugin exist? (or are you struck by inspiration?)

Does an alternate CMS that does this exist?