I discussed this with @codinghorror and we would like to hold off this work before some other work happens.
In particular group management needs a serious iteration first because it is required for this work AND blocking lots of people.
@lightyear started some work on Improved Group Members Management but it is not fully done. There is no easy way to manage a group with more than 200 users the UI does not scale.
Additionally we really want the concept of “group owner” first, which basically gives a normal user the ability to add and remove users to a group they own.
We need the above properly specified before working on the full blown “category moderators”.