Photoshop: new layer style: Motion blur

Layer styles are useful because of their parametric and their non-destructive natures. Smart Filters are useful, but require the creation of a smart object beforehand.
I'd like to suggest new layer styles, of commonly used effects, that would help to automate time-consuming tasks.

Motion Blur would create the effect of giving impression of movement of the layer.
-one should be able to control the length of the blur,
-the starting point or blur edge (so that the whole object/layer would not be blurred by the motion blur, but only part of it).
-the blur edge could have two settings: flat or parametric. Flat would blur gradually from a given point, while parametric would fade the blur according to a fixed distance to the edges of the layer (to be able to have a sphere whose motion blurs follow its contours).
-the end of the blur could fade with desaturation, and opacity.

It would be very useful to be able to create a path that the blur would follow, but I'm not sure about the best interface: on the image, or in a dedicated widget (I prefer the first one).

I hope that other users will chime in with proposed refinements, or additional (useful and feasible) layer styles they'd like to see.