Since "anything goes" is the mantra... Had this idea for a while when the game was live.
An evolution of SHIFT-Drag, I thought a "pseudoplane" (for lack of a better term) might make floated object placement faster. Either a mode switch to turn on a slider, or a Z-Index input box that has two up/down arrows (one for fine control, the other "snaps" to common heights equal to counters, desks, or another object you can pick). This way, every object you place is only on X and Y placement no matter where or how you are, and Z is directed by the pseudoplane control (every object you move or add floats by default at the given level). The UI could be a glowing grid at the pseudoplane level (the lit up area being the 'floor of the plane'), or visible only when placing an object, or a 'laser line' around all edges of the room indicating it's on. Or nothing, it's just on or off.
Questions: would stacking still work on the pseudoplane, thereby making it not 100% effective when building close to floated objects, or would stacking be defeated in programming (if that can even be done)? An annoyance to turn pseudoplane off when you DO want to stack, so I could see that as a downside to the approach. Also, negotiating X/Y limits like doorways. Finally, I'd imagine a one-button kill switch would be needed for it in case something places wrong and pseudoplane screws with the repair because you grabbed an object NOT on the plane and dragged it up, or could it only allow new items to be placed and not affect existing ones? (Again, is that even possible to program into the behavior?)
Why? The ability to build pseudo floors quickly from room to room. Or having objects at 2-3 fixed levels floating above (Harry Potter-esque lighting over dining tables) executed consistently from place to place.
There's my idea.