But how many people actually use the Volo screens? Not many, judging by walking through Coach D or past it on a platform.
But there may very well be serious structural issues with adding more/bigger windows. Indeed there's a letter in October's Modern Railways which says that those half-screens mid-way along Mk3 interiors do in fact have a structural role - but looks like no-one told whoever designed FGW▸ 's refresh...
Redundant buffet cars
have been converted into ordinary trailers previously. Two were converted to Trailer Firsts as insurance replacements for the two leading coaches destroyed at Southall.
I understand FGW consulted the surviving members of the team that designed the Mk3's and confirmed that although the mid car screens in each trailer were supported on frames welded in at the construction stage they were not critical to the design of the vehicle or its strength. In any case they would only provide very limited stiffness in terms of bodyside movement when trains pass each other and would not affect the ability to withstand vertical loading or bending. Or buckling of the shell in a rollover / collision situation.
On the class 156 Mk4 derived shell the mid car partitions are structural to the coach.
The question of structural integrity on buffet cars depends on what longitudenal 'top hat' sections are present underneath the skin and below the window line of the small windows. And whether the bodywork can cope with their removal. Obviously the bending loads are less with standard trailer vehicles than with buffet cars with most of the catering equipment weight in the middle of each coach. I understand as much as anything the electrical systems are as great if not a greater problem than making the bodyside wiindows larger.