I think there are multiple forms of solid volumetrics and many ways of doing it and different nations would use this technology for different purposes. I really like the idea of diversity, with different styles of volumetrics used for different things -- and I'm really glad solid volumetrics are finally being explained.
I really like how you've gone with the approach of explaining it as being like a cathode: drawing geometry to form topology and three dimensional shape rather than 'pixels' in the most classic sense which would have very limited resolution. Here, the limit is the geometry count of the projector and the processing power of the computer linked.
You should explain whether irredesance (ambient light affecting the perceived colour of an object: for example, red light making a white object look pink) is simulated by the computer based on observed light-sources OR if its actually done by making the solid-volumetric scatter light realistically. Unfortunately the problem here becomes that stuff like sub-surface scattering (which produces changes of colour inside an object like wax or skin or moltern rock) isn't possible with incredibly thin layers and would instead have to be simulated.
This unfortunately means that a means of checking whether or not a solid volumetric is real exists: Is the sub-surface-scattering reacting in real-time with light-sources it can't predict? If it can't, its going to look very very ghostly in those rare artificial circumstances -- but it produces a means to identify whether or not a projection is real quite easily -- which could be a fun thing to note down for roleplayers in the event they need a low-tech way of figuring out if the person they're talking to is real or not.
Coming back to the point of diversity, I'm developing "
hard light" with Lazarus. It works very differently, by tricking photons (light) into linking and slowing to a stop so they behave like baryons (matter) with the same repulsion effects so matter won't pass through it. The downside is unlike Solid Volumetrics, it needs a sustained projector to work.
Its more designed to be used akin to the structural integrity fields of Startrek (like hot-glue holding battered and wrecked things together made out of light or akin to cellophane stopping a cake from crumbling if you throw it into something) or as an active camouflage pattern or for arranging and assembling makeshift tools than as an input device or as an extra layer of armour or platform or wall.
This way of using volumetrics and light in different ways in the setting seems like a natural evolution of any sufficiently advanced technology. I really like it.