The following nodes setups aren't real shading but a simulations. In fact these are a bit more of a proof of concept, but can be used to some degree so long you don't mind limitations. These were designed to get more control on the color of objects similar to what was possible in old Blender Internal.
Sadly some features are lost: Light sources are limited to the ones provided (1 light source per material) No shadow reception by the texture shading, they can be added back by replacing Flatshader with Diffuse or Toon shaders or others. Not perfectly accurate shading, not sure why. Poor previewing
SUPER Important considerations for sunlamp and point lamp: Rotating and moving the object itself works fairly well, but moving and rotating light source is very heavy for Cycles for some reason and it doesn't update he 3D viewer nor the render preview UNLESS you go back and forth from render preview to wireframe... yes it is super weird/annoying I know.
Details: There are pictures with quick tutorials, check them out! Of course, it can be used along freestyle, in fact I think it will benefit a lot.
NPR Flat shader is shader designed to produce flat colors in the renderer, the "bounce light" value can add or remove some integration to the scene if needed, its very subtle
NPR Ourliner shader is meant to be used with inverted hull technique, check out the modifier and materail setup of the provided cube. Only for silhouette and some creases.
Tex Classic Open GL Sun/Point: texture based lighting that can be used to mix in RGB the simulated light sources using mostly color ramps and mixRGB nodes, they can be mixed with textures as well, in the case of "point light", disntance can also be used but maybe you will need to get inside this node if you need loner distances. These nodes NEED vector inputs to work correctly.
Vector No Image Normal Input: if you don't need Bump maps or normal maps then use this node for the above Classic OpenGL Shadings textures.
Vector Matcap: this node can convert any texture in Matcap, I added because.. why not?
Last words: Hope it helps and you like them, this should be the last time I release these since I'm thinking on an alternative way to achieve these result in a next version, but dunno when it will be ready.
Version file v1.1 March 21 2018, ViÃÂ±a del Mar, Chile.