on Alstom's site:

http://www.transport.alstom.com/home...=EN&dir=/home/

"At the heart of the train architecture is Bogie Offset Articulation which
reduces the number of bogies by up to 30%, allowing the carriages to be
shorter and wider and thus optimize the vehicle gauge. This in turn creates
more passenger space and comfort. A wide, uninterrupted aisle and spacious
gangways are created throughout the train, improving the feeling of security
for passengers as well as mobility."

"Safety onboard is increased as the energy absorption areas are concentrated
in the elongated front end of the train rather than between carriages,
making these areas safer for passengers and crew."

"The door configuration is geared to reduce stopping times at stations by
making the boarding and alighting process more efficient, particularly on
high-density routes. Two sets of double doors are situated in the centre of
each carriage, providing 25% more doors than a conventional trainset, per
equivalent length. The shorter carriages of X`Trapolis are also closer to
platform edges, especially when these are curved, reducing the stepping
distance from train to platform by almost half."

I reckon there could be some debate about the door setup, I don't see how
two sets of double doors in the centre of each carriage provides 25% more
doors than a 1/3 - 2/3 set up, unless of course the carriages are somewhat
shorter than 20m...

Alstom themselves don't explicitly mention Thameslink/Crossrail, but
according to the FT:

http://www.ft.com/cms/s/0/6dfe18d8-a...44feabdc0.html

This closely follows Siemens and Bombardiers offerings, the Thameslink
decision is imminent IIRC...

Paul S