No idea what you were trying to demonstrate - you posted without giving a link to the Tripadvisor thread (if you are referring something it is hardly a stressful task to give a link, is it?) and just said it was headed 'GWR's new trains' - which might tend to suggest that all the posts covered by the list of numbers were about GWR's new trains, except they weren't.
Could you actually explain why you think the five-car sets should be extended to nine-car sets.
There is no way on earth that large numbers of the services that the IETs will be working for many years will ever need a 630-seat train - a fair number of the five-cars are replacing 180s and Turbos or providing new services such as the hourly Cheltenham-London frequency and the extra 2tph limited-stop off-peak trains between Bristol and London.
If the entire Bristol service was worked by nine-car sets, you would be offering 2,500 seats per hour in either direction all day. Good luck with getting enough bums on seats to come even close to breaking even on the costs of running that lot up and down.
The full IET fleet already provides a substantial capacity increase on what it is replacing. At a time when growth in passenger numbers has pretty much stalled across the network, proposing massive over-capacity is not a great idea.
Although the questions weren't aimed at me there's two thoughts on this.
Firstly not so the 5 coach trains would necessarily be lengthened to 9 coach units, as such it could be an extra 6 which are lengthen, which would provide some extra capacity but wouldn't make it so that there was far too much capacity.
Secondly, we mostly only have the headline figures on passenger growth or lack of it. A lot of the do is associated with a few TOC's the largest being SWT. What had changed in terms of extra trains in the last 5 years at SWT? Until the Waterloo rebuild, not a lot a few extra trains on the busiest network in the UK.
Is it therefore surprising that passengers aren't studying around.
Even on the wider network there's not been that much in the last 5 years which has substantially improved things for passengers and much that has will have been in the last year. Yet for much of that time passenger numbers kept on going up.
Once things bed in and there's more visible improvements I wouldn't be surprised if there's more growth again.
The network is creaking, as we are broadly at the number of passengers expected for the opening of HS2 phase 1, yet there's not been many major (fully delivered) improvements for several years.
