Agreed. CC-BY-SA is the default license for sketches created on both SketchPad and OpenProcessing, which makes modifications and cross-polinations possible. I discuss a few of the possibilities on the sketchpad blog (which is currently in a half-functional state): http://blog.sketchpad.cc/2010/05/default-cc-by-sa/

Keep an eye out for clone/fork functionality (but don't hold your breath for a merge option.)