Why did Telgo make shorter coaches ? with reasonable idea that it will be easy to haul them than larger ones...
and this is right choice if it is size...
Not why to increase the length...
In future short size coaches will pave the way for selective augmentations of coaches depending upon the 'booking rush' ... it is as good as pressing in...
more... more buses whenever passengers are more...
But the idea of 'berth weight plus passenger weight' is still too early to down play ...
As Car technology also is gradually using more of plastic and amagmated metals in place of original iron casings in body and engines ... So is with aviation and Shipping... to save fuel and increase speed...
So weight is always the problem whether it is 'own' (coache) or other's (passenger)
Still your explanation is very logical... I like ..