Very clever.
You could also combine this with some additional mechanics to build a device for specifically destroying certain objects. In place of the first stockpile (where the objects are dropped) place another floor hatch, over an atomsmasher or magma lake or something. Now, you'll need that hatch to open only after an object has been dropped on it, when the dwarf is walking away. Something like so might work:
#####
+D^D#####
####^hhs#
+++h#####
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Here the dwarf enters through the southern chamber, heading for the stockpile. He walks over the closed floor hatch in the southern chamber, then steps on the pressure plate. This opens the floor hatch in the southern chamber, the floor hatch just before the stockpile, and both doors in the northern chamber. The dwarf proceeds onto the still-closed floor hatch just to the east of the pressure plate, then stops because his path is blocked. Job canceled, the object gets dropped, and the dwarf heads back out of the chamber, by the now open northern path. On the way out, the dwarf steps on the second pressure plate, the one in the northern path, which opens the floor hatch that the object was dropped on. The object falls into the atomsmasher or magma lake or chamber containing a burning plump helmet man or whatever.
The two doors in the northern path stop any dwarf from stepping on the second pressure plate except just after dropping an object on the floor hatch it controls.
I haven't tested this in-game yet, but it should work. By adjusting what is permitted in the stockpile, you can use this to selectively, automatically destroy a specific class of items. Sub-masterwork furniture, pig tail socks, dimple cups, whatever you don't want around.