I think the only way to properly solve the undump's problems are to find external ways to get dwarves to drop their hauled item, external meaning they cant be standing on a pressure plate, since getting junk off a pressure plate either requires flowing water or a door/floodgate immediately underneath the pressure plate which was originally created on a now destroyed wall. Flooding is a pita, and will never work on heavy objects, and its impossible to get dwarves to path through unsupported pressure plates.
So lets list out ways to make dwarves drop what theyre doing.
1. No path -- this is what the undump uses, and what some of my earlier science worked off of, its major downsides are reduced stockpile size if the whole thing gets blocked off, or major lag if its a repeating trap. Eyeglazed's work on creature timings has pretty much convinced me its impossible to make a pressure plate hallway that will make all dwarves drop their stuff while still allowing dwarves outside to continue pathing towards the stockpile without a repeater, and to me that means heavy lag.
2. Scaring -- So I think the scare dump is a definite move in the right direction. It seems quite conceivable that every dwarf heading towards a stockpile with a chained creature sitting on it will drop his stuff, assuming proper window placement. Then its just a matter of setting things up so that the tiles dwarves drop food on are all hatches or bridges, preferably controlled by the exit of all dwarves from the hallway. Unless youre dropping into magma, you can always have my patented Duck Duck Goose failsafe system, where stupid dwarves who fall in the chute land on fluffy ducks and gooses instead of exploding, and yes, pastures and stockpiles can be placed in the same place.
3. Dangerous Terrain: a dwarf who finds himself in an unpathable tile will cancel his job and try to path out of it if he can. Unfortunately, they dont always remember to drop their stuff immediately. Dwarves can be put on unpathable tiles by making them fall onto wall grates, vertical bars, or (iirc) fortifications. You can also flood the tile theyre in/about to walk into. Since making them fall has many of the same problems as method 1, maybe we should look into repeating mist machines to cancel their jobs? I dont know if water forces pathing to be recalculated, or if its more of a OH NO IM DROWNING moment, so im not sure of fps woes from this...
4. Does combat make them drop things...? I know Ive had a marksdwarf drop her baby to the carp while reloading, ( the carp was 3 zlevels to low to attack, and carp cant fly, she had only herself to blame that time). If so, we could just put a bunch of repeating training spears in the hallway, then dwarves will dodge fall down a level, creating a one way path and making their original job inaccessible, more so they drop their junk and head towards an accessible meeting hall, except whoops, they trigger more spikes, to drop them back to fortress proper, and then a plate that dumps their junk. All the falling, hopefully none of the recalculation of pathing that kills fps.
5. I dunno, what else makes dwarves drop things? How long does it take before they notice theyre on fire? Are there any syndromes to make them pass out that we can then power wash off them to wake them back up? Ideas peoples!!