It kind of would contradict the game title "2D".
But one thing that annoys me and much mappers i presume, is making 2 floor houses and stuff, like, if i make a map with 2 floors and a balcony at the 2nd floor that is able to see the lower floor i can't see or shoot people from there, and this makes the gameplay of 90% of my map ideas that would be great be a crap.
Ex.:

This way i can't see who is at the lower floor.

This way i can, it's like a sync. between the 2nd and the first floor, there could be a tool in the editor to set what places would link with others.
It would help a LOT, but i presume it's hard to implement