I've needed more than one time to be able to fill a shape with 2 or more colors following the form of the shape, to get that I have to use for instance contour + feathering or transparency to get the result.
I think that have a "shape fill" (as we have, conical, circular, eliptical, etc) would be great.
I hope you be able to understand my explanation, it is a bit difficult to me to explain.
If you need more detail I can make some drawings to explain me better.