Painterly, watercolour and stroke based rendering
First, an article, a collection of the state-of-the-art approaches review for Painterly Rendering.
The research article appeared in Computer Animation and Virtual World Journal, Volume 24, Issue 1, January/February 2013, Pages 43–64. A very detail read.
Second, a paper by Disney Research titled OverCoat: An Implicit Canvas for 3D Painting
You can paint painterly strokes on a 3D mesh much like Deep Canvas in Tarzan.
Are these the paths Blender’s Grease Pencil is going next? Who knows, we are open for discussions.