pit cover
acts as pressure plate for triggered by creatures only.
when triggered it deconstruct back to its component parts.
can be made from wood.
yes it the old put branchs over pit trap.
I like it, but it's extremely powerful. Dropping enemies down a shaft is good enough to make the bridge+pressure plate worth it even while being so hard to time correctly and so dangerous for your own dwarves.
Creating the same effect with such an easy contraption would be too much.
Being able to build one of the simplest traps in history simply is going to far? Elaborate, please.
I think the added micro, from the deconstruction, would make this more something that people do in the first couple of seasons, before the mechanics industry is a priority. Once you have higher quality mechanics and mechanisms, you can build something more elaborate.
If it makes you feel better about the Rube Goldburg method you currently use, we can say that simple pit covers destroy the wood used to make them. It's realistic enough to be justifiable.
Additionally, you could make flows and whatnot also break the pit cover. If it's properly flimsy, it isn't going to stand up to a flood any better than a kobold's footstep.
Though, being able to build a proper, single-tile trapdoor would be good, as well. No one is even going to pretend that traps are balanced right now, so we should focus on coming up with things that are fun and fitting, and then worry about balancing them. Trapdoors are a huge staple of the genre, and they're schadenfreude-tastic.
You could build it out of a hatch cover and two mechanisms(one for a pressure plate, and one for a door opener), over any sort of gap in the floor. When you step on it you have a short time, based on the quality of the mechanisms, before the hatch opens, and anyone on top risks falling fall. Fast foes will be basically immune to all but the best trapdoors, unless they happen to step on it after it's been triggered, but before it falls.