Being able to paint decals with special colors would be amazing however I can see it being very demanding on the servers from a technical standpoint. Those color schemes are a lot more detailed.
It's not really about it being demanding on the servers.
The way I understand it (and I will happily be corrected)... It looks like the SVG files are converted to raster images before they are applied to the car (at varying resolution depending on the game mode). Since special paint effects can not be captured in a raster file, there is no mechanism there for the game to know you want something to look chrome, because neither an SVG or JPG/PNG etc. file can store information like that. In simple terms, paint effects are not colours, they are rendering techniques.
The paint effects have to be linked to the car model so that the games rendering system knows how to handle the rendering effects. They clearly do do something similar because we can set if all the decals should be matte or gloss, but the fact it only lets you apply one setting to the whole car makes me think it's not that easy, and, if you've ever done any 3D rendering, you'll understand that some effects are much harder to achieve than others... these are the settings in Blender for instance...
... now, PD can obviously provide all the complex settings as presets for each paint chip, so it's not like people would have to understand all this stuff... but my point is that settings like this relate to the 3D model of the car
not the individual livery items, and that it's not really server load, but load on your PS4 and the game.... imagine 300 layer decals all with special paint effects on each, on all 20 cars on the grid... 60 fps... more like 1 fphour!