The prototypes I saw in person a few years ago were actually surplus automated potentiometers :) They were DC motors with gear reduction and a spool, with light steel wire coiled on the spool to slide the pot or the "3-d pixel" back and forth. these may very well be pneumatic.
True, although oftentimes way slower and getting the types of feedback they were using in the video would be tougher. On the upside, I'd expect this would work far better for heavier objects.
A regular threaded-rod would be slower, but you could speed it up by using a different thread profile with a longer pitch. If speed was the top goal, though, a belt-driven system could be as effective as pneumatics, but quieter. (But then you can't hold weight when the power is off.) Lots of trade-offs to consider, depending on design goals.