The problem with this is that our art resources are very weak. We don't even have a single dedicated modeller at the moment. I guess i come closest to being such a person, and my output rate given my current schedule is 3 models per *year*.
If you want the game to have better visuals, the first thing to figure out is where to find people to improve them.
Models wise, i've had a fairly decent experience with directing an outsider artist to produce a high-quality model from concept art and a long list of requirements (tank factory) that fits the game very well - so perhaps just finding some modellers would be sufficient. So for models, it is maybe possible to actually commission artists, if you've got big pockets.
Shaders are more difficult. Especially since having all the really fancy things requires a quite lot of changes to the engine and the game. E.g. a modern, gpu-based particle system would be a massive improvement over the currently used CEG and LUPS particles, but for that, not only you have to completely implement a major engine system from scratch, but also you have to reimplement every particle effect ZK has in this new system.
I would say also that one of the things that units mostly miss is good animations. Sadly, Spring doesn't really support easy outsider contributions to animations, because Spring animations are
code that is run in a
synced context. There are some crutch tools that allow you position the pieces, and i wrote a Blender addon to allow animation exports from Blender - albeit lacking a lot of major features modern animation software takes for granted, like bezier interpolation. However, my experience with directing outsider animator talent was a lot less stellar than my experience directing model work, in large because the entire animation pipeline is garbage.
I will illustrate the animations point with this. Compare and contrast this with the lobsterly nerd pose that the Strike commander strikes when shooting in the actual game presently.