I hope people are still around to give me some input.
1. With Pages, I take it you mean Pages not Blog Posts
I'll start with the assumption we're talking about pages, not posts. If this changes I'll have to revise some of the ideas

I can see two ways to implement something like this:
- You can select which categories are relevant on a page by selecting them on the Add/Edit Page page.
Only the selected categories will be displayed, no hierarchy. - Use category groups defined by the plugin which you select on the Add/Edit page
Only the selected categories will be displayed, no hierarchy. - Use the Parent/Child categories. You select the Parent category on the Edit/Add Page page and all it's children will be displayed.
Cons/Pros:
1. Pros: Easy Overview of which categories will be displayed for that page.
Cons: When you have a lot of pages and you want to add a category you need to edit all the pages.
2. Pros: When you have a lot of pages and you want to add a category all you need to do is add the category to the group and your done.
Cons: Extra administration
3. Pros: When you have a lot of pages and you want to add a category all you need to do is add the category to the parent and your done.
Cons: Can't mix categories from different parents.
I'm personally leaning towards #2, especially if you guys don't mean Pages but Posts as a page
By all means this is not a final thought, I need some help with this as I can think of three ways to implement this already.
As far as a time frame for implementation, I can't really give one unfortunately. Holidays are coming up and such.
There will be a 3rd widget, there are 2 now, that will accompany this implementation.