Originally Posted by Jiggle

I just can't wrap my mind around how that would be a benefit. Maximum bending stress is on the surface of a beam, and making it thinner brings the point of maximum stress closer to the neutral axis, reducing stiffness. The thicker upper and lower would add nothing because the reaction force is at the thinnest point.

Might as well just make the whole sidewall thin.

Which is what we see in modern rims.