I like this challenge 
Here’s my version…
I’m driving it off what you actually see in the view… ie. the cut surface of the wall… (incase you have a wall which is inside in this view but not entirely inside the area solid, perhaps it spans several levels)…
This option might be worse if you only want the ones who’s volume IS entirely in the area solid 
Edit:
Slightly refined…
WallCutByAreaRegion.dyn (19.7 KB)