Chris Montesano provides a sneak look at an up and coming Node based Shader System for Cinema 4D in his cmNodes. The cmNode Editor will allow you to create node based shaders trees, stringing together attributes, effects, materials and shaders providing a nodal approach to create shaders in Cinema 4D.
This is a preview of a new node based shader system for Cinema 4D, coming soon
Certainly there are limiting factors to not having access to a nodal based shader system; Nodes allow for the creation of some complex systems building and expanding on the tools that are already available by chaining inputs and outputs together in creative ways.
Not much is known about cmNodes at this point, other than it does seem to work with V-Ray Shaders, and that the nodes integrate with Xpresso by drive any Xpresso node parameters, however, you are not able to connect Xpresso nodes to the shader tree or connect nodes together via Xpresso.
