I don't have suggestions for an interface, but why not just start with a SpecialPage and see what happens? Once the functionality is there, suggestions for how to better use it will come out of the woodwork.

Several of us at Wikipedia did some work on an interface for incorporating category intersections a while back. It can be found at shortcut [[WP:CI]] or full url:

http://en.wikipedia.org/wiki/Wikipedia:Category_intersection

--Samuel Wantman [[en:User:Sam]]