@ShadeHawk : true, however there's two factors that make that impractical for the natives (read: the Skaven) even if they should think of it- firstly, Dungeon rooms-
especially their outer walls- are 'naturally' more durable due to being saturated by the Dungeon's mana, making them extraordinarily difficult to tunnel through. this is a good thing, too, else the main cavern, which, I'll remind everyone, is a
sixteen acre bubble, would collapse in on itself at the slightest provaction. The second is the Dungeon's... I suppose
contour sense would be the best description, which absolutely would detect such tunneling efforts nigh-instantly. Also remember that these things are all build on solid rock, not an easy thing to undermine in the first place, even without the aforementioned.
as for Unsummoning, perhaps I should say that there's no
practical means to do so. antimatter, for example, would either require more mana than I'd get out of a reaction if summoned in a containment device, or require a large vacuum chamber and some quick hands on a containment field, due to the limitations on
where the SI can summon raw materials with arbitrary properties; namely, only in a room that has a Relay or Core in it.
I imagine I don't need to explain how having a bunch of air around for said theoretical antimatter to
react with would be...
bad.
the only way for the SI to really pull that off would be to tech up to an antimatter Breeder of some sort and use a relatively mundane power source to run it- ironically, the way summoning complexity works Coal runs mana-positive while more sophisticated fuels like petroleum would 'just' run mana-neutral, mostly because mechanical force isn't 100% efficient, so you'll always lose some energy in the form of heat, or friction/inerta resistance, or transmission loss in electrical wire, and so on and so on.
the upshot of all this is, the SI can't just wave a wand and clear away debris, they have to have minions actually clear it away by hand (or bulldozer, or whatever) and actually have somewhere to
put it after doing so.
Plus, the SI can't direct-summon into an area that's under attack (things under a Relay count as 'different areas') so anything reliant of such would instantly shut down, barring unit-producing Features such as Workshops- those, however, have limited ability and can summon only certain parts or materials.
oh, and there's no 'research' screen either, minions have to do that essentially the old-fashioned way, allowing for the Dungeon's buff effects making them the near-equals of Kushani Science Bullshit in terms of turnaround time.