Since I first started having a play through using the Under-Cities and Vampire Coves mechanics with Skaven and Vampire Coast I have always thought that you should be able to view all your hidden settlements in a menu similar to how the dark elves can view all their provinces to manage slave income in one menu.
Currently if you have sent agents out and established many hidden settlements all over the campaign map its easy forget about one or two and not build it up properly. So if you want to check them you have to zoom out go around the campaign map and look for icons over the settlements that shows them and as you get a larger amount of them they become more difficult to manage. I believe this would be easier in a menu.
In a menu for the Skaven you could include for each Under-City how much money+/-, how much food +/-, how close it is to being discovered, etc. Then you click on the settlement in the menu and it will zoom to the location on the map so that you can build any required buildings.
What do you think and would do it differently?