One thing that bothers me about this and other recent EMU orders is that we seem to be sleepwalking back to a 20 metre coach length.
20m is dictated by approaches to the south London terminals, hence Thameslink (319/377) and SWT (450 etc) specified this length.
These constraints don't apply to north London terminals or elsewhere across the country, and most services are today operated by 23m trains (eg DMU classes 158/175/185, EMU classes 323/333).
LM ended up with 20m 350s only because this was originally an SWT 450 order diverted to the WCML and reconfigured.
But now we seem to be ordering more 350s and 377s which will be working well away from the 20m limitation.
Why are we giving up the benefits of longer trains, in terms of capacity and layout, when there is no need?
If the newly electrified lines all end up with 20m stock I think we will have missed a trick somewhere.
The "cost per seat" in 23m trains must be less than that in 20m trains.