As a weight engineer, i understand that weight is directly proportional to performance. That is to say, airplane, train, bus, or bicycle, the less weight you haul, the more you save on fuel.
Since we want to haul more people and their stuff, the best place to save weight is in the structure. They need to be considering aluminum frames, or even just where they feel structural integrity is not an issue. The cost of the material should be offset by fuel savings.
The other performance improvements come from aerodynamics. Unfortunately, no matter how aerodynamic the Amcans are, all benefits are destroyed by that hunk of P42 out front.
So what is the answer? I dont know, but i for one would really love to see a uniformly consistent height consist, functional and weight optimized.