I think we just need velocity to movement, and we could have the camera do it. Like i mentioned, it's all done at a frame-by-frame basis, so it's speed is derived from frames.
If there was velocity, than things could be moving faster than the frames and it may work. Even in blender the motion blur, or normal blur is just on the camera level, and to not blur other objects you move their object ID/Level below the camera's so it's not effected by the camera. (Kinda like Z-Index's in web and such)
Object blur would be cool though, I can see lots of uses. Like the planes I wanted to use at all sorts of distances without doing post on them all lol