You mentioned winding numbers in a couple of places

Wouldn't it make sense to do a "first pass" and eliminate paths that intersect themselves? (by splitting them into 2+ paths)

I never understood why these are supported in the SVG spec.

It seems like a pathological case. Once self-intersecting paths are eliminated the problem gets simpler.. no?

Or would a CPU pass be cheating?

The Rasterizer algorithm handles self-intersecting paths without issue. Removing them requires expensive and complex computation geometry.