The worst part its that there is almost no doc on how to do it, no to mention 0 official doc. It would be very helpful to document shading models or vertex factory modifications + without recompiling the engine (Its doable in other engines without much effort).
Unreal has all kind of shading models but somehow a basic toon model is missing even though it has:
eye / clear coat / three SS models (Subsurface + preintegrated skin +subsurface profile)
Why do this models have higher priority than a toon model in a supposed “general purpose” engine? Do most devs really need a clear coat or an eye shading model ? “but you CAN modify the engine right?”
The sad truth is that unreal is not a “general purpose” engine when it comes to visuals, “photorealistic” rendering is THE goal and its probably a design/marketing choice. Anything else has to be an unoptimized workaround within those limitations or engine modifications( with all the problems and costs it implies).
Ironically this is making most UE games look the same. I dont think thats a minor issue.