@DMofDarkness: Though the idea is good in principle, I have to agree with everything Owrtho pointed out. It is impossible for an underground district to be as extensive as you say this one is, especially if you want it to be unknown even to The Eyes which in itself is an impossibility. If there was something that large that The Eyes did not know about then they would not be doing their job very well and would indeed have been utterly useless from the get go. The whole point of them is that they know or can find out ANYTHING.

Also you seem to be assuming that all these aberrations would A. all have an interest in Ishka to begin with (Plausible) B. would all be as evil as they're painted in the MM (Myth Busted) C. would not have fond a way to work together not only with each other but with the rest of Ishka in a reasonable manner (Myth Busted)

All that being said I think there should indeed be an Aberration District (with a better name than "Aberration District") modeled after The Necropolis, only for Aberrations instead of Undead.