I think it would be nice to have one-way walls for our condos.
Right now it is possible to create a one-way passageway
as shown in this video
but I believe it would be nice to have an item for this so we can do it on a large scale without having to look at a ceiling fan in the wall as shown in this bug.
You can walk through the wall one way,
while you get blocked on the other.
These can be used in conjunction with one-way wall textures as well (where one side is invisible and the other is a specified texture OR you can use a texture gun to specify textures for the 6 different sides of the wall).
One-way doors could also be useful (doors that open from one side only). You can use a timer (with Condo/IO) to close the door automatically as well.