How about a lenshood that "changes" its shape as the focal length
changes? The shape of all lenshoods for all lenses is obviously
optimized for the lowest focal length of the zoom setting. Once you
move to a higher focal length, you could have a longer lens hood
(which would be desirable as it blocks more light).
One way to achieve this would be to have integrated lenshoods as the
200/2.8 Mk. I, or the 300/4L. You "activate" the lens hood by turning
it until some mechanism locks it. The hood is connected to the zoom
ring, and as you zoom, you "zoom" the lens hood as well.
Christian