In my opinion, the strength of 3D printing isn't just about printing parts, or multi-color/material parts, but being able to create new materials (composites) that couldn't exist without the processing method.

One of my projects is looking at 3D printing of multiphase materials. This is a single print head, but we're mixing two different molecular weight polymers and an inorganic filler. The goal is to be able to use the ink parameters and the printing parameters to control the distribution of parent phase and filler. Effectively we want to control the internal structure, to control the properties. For example, we could possibly print a material that is highly conductive in one direction, but somewhat insulating in the others. This type of microstructureal control isn't as simple to achieve when using other processing routes.