All this talk of priority boarding, of sunflower lanyards, of "baby on board" badges, and no doubt other schemes is all trying very hard not to admit that there is an underlying problem with new shorter trains.
I doubt anyone on here is surprised you've drawn that conclusion.
But a few facts to counter your suppositions:
1) 19 of the 20 trains selected for the trial are booked for either 9 or 10 car
DMUs▸ , which of course have around 20%
more seats than the previous DMUs that operated them.
2) Those 19 are all allocated 9 or 10-car trains as planned today. It is of course possible that some unplanned shortforms will happen on occasions, but not today at least.
3) The trial covers two trains per hour, at half hourly intervals, and includes all of the trains from Paddington to the West of England bar one between 09:04 and 19:04, with additional Bristol trains on the hours when there is no second departure to the WoE (at 11:32, 13:32 and 15:32). I expect those Bristol trains have been chosen because it would be difficult for the team doing the trial to deal with departures that were not evenly spaced every 30 minutes or so, and not because the 13:32 to Bristol is a particularly busy train. The slightly odd omission from the list is the 17:36 to Plymouth, also booked for a 9-car.
4) The one train booked for a 5-car half-length train is the 11:32 Paddington to Bristol service. That's currently running to Bristol Parkway rather than Temple Meads, so I will check to see what formation it is booked for when it resumes to the normal timetable.
Oh, and I find sunflower lanyards very useful in giving me a visual alert that a passenger might need more assistance than is typically the case. It's a national scheme, not specific to the railways, and certainly not dreamt up by
GWR▸ to try to cover up for half-length trains.