Potential ideas:
May i suggest that testing the effects of burning/magma (and settings) on biologicals (dwarfs/nobles/elves/gobs) with and without netherwood as impromptu "passive"-shielding. EXCUSE FOR BURNING !!SCIENCE!!
And of course...the magma digger contraption..it doesnt dig magma...it digs WITH magma..i would suggest using it to dig ice somehow at first
(maybe with some subjects for a steambath too)
The creature sorter..using water to sort them to various "good places" (probs need way to save babies from it too unless you dont hehe)
Insanitarium a "device" to help various entities go insane in whatever ideal ways. And ways to carefully (or with FUN!) finish them off.
the opposite of an Insanitarium..a "device" to keep entities sane and healthy however in the smallest minimal space (excepting just staying in a cage)
Pond-erizer a contraption to train air breathers in swimming...while they are in a natural dwarf fortress pond (and keeps them there long enough they got some skill) Bonus points for figuring out how to get it to train other things too. And yes this means without removing any of its "natural slopes"
The blender- simple and easy way..to make a drowning area that using the pressure of that water coming in chop them up for the maximum "blending"
Spy vs Spy rooms (spys that bomb/stab/otherwise try to kill each other at same time)--better if they actaully benefit the fortress
1st one...two rooms...each makes the other room puncture the spy within til one is dead.
2nd ideas?
the Freefall gadget-so simple so elegant so stunning that you can get into freefall (yes this one is known..lol)
Pingpong Table..turn entities into the ball Suggest 3+ levers(or other subdevice) for each side to help control it.
1 Prelaunched Arrow defence and 2 automated defences turned on or off by archery practice..sounds silly..but figure out how to turn archery practice into something more than mere practice and the known practice arrow retrieval ideas. Ideally would have minimal dwarven death