Reading a copy of Radio, Television & Hobbies (Electronics Australia) from July 1958 I was surprised to find an article on page 27 describing, along with a couple of 3D glasses techniques that have continued to intermittently haunt cinemas and homes ever since, a colour 3D display in a design that might today be better described as a volumetric display.
The experimental device used apparantly solid-state "electroflor" substances what glowed different colours when stimulated at "fairly low voltages", mounted in glass plates which could be stacked to create the 3D display area. Presumably there were some down sides to these "Electroflors", or else CRTs would have been much shorter lived, but I wonder why the same approach hasn't been used with LEDs.
I'm guessing that the Electroflors didn't produce light directionally like LEDs, but wouldn't it be possible to mount lens elements inside the glass, perhaps existing wide-angle LEDs? The wiring and glasswork would probably be well above a DIY project for something with a decent resolution, but why exactly couldn't these be made much like LED TVs, except with the LEDs pointing to the side and shining at a wider angle? Even blocks of six LEDs making up a cube?