Trying out the scribble fill method from this old Apple patent by John B. Turner with a bit of spline embellishment at the corners. Seems to work pretty well for more convex shapes, but results can get weird otherwise (the Olympic Peninsula seems especially uncooperative).
Some possible tweaks:
- Drop any orphan scribbles with only two or three vertices
- Add some random control points to make the scribble segments a little swoopier
- Add a hand-drawn effect with SVG turbulence/displacement filters
- Select intersections based on a more simplified outline of the shape