Similar functionality to grease pencil can be derived by using the TriPlanar Primitive. Perhaps by adding some presets and options to that primitive a grease pencil like effect can be more easily simulated. For example a TriPlanar primitive with a short Zdepth that auto populates facing the camera with an adjustable transparency.
While grease pencil may not be useful for 3D modeling, it can be useful for concepting scenes in 3D to work out perspective for 2D artwork. Obviously there is a demand for it. Just look at uMake and Gravity Sketch.