Whilst escaping from rain in Euston today I popped in to see the model.
Amongst the features of interest:

* The carriages have a strong overground feel to them, both on the outside
and inside.

* The carriages are linked like current DLR cars and trams with passengers
able to walk the length of the train. This may, however, make it impossible
to have a half-length train for Chesham - see below.

* There are door open buttons - will TfL ever make up their mind about
these? - but no, as far as I could see, door close buttons.

* There's a mixture of seats including sideways, cross ways and fold down. I
have to say I don't like the angle of the seats for long journeys on the
Met.

* The seats are attached to the wall rather than the floor, allowing bags to
be put under them.

* There will be airconditioning on the trains, taking advantage of the old
arrangements in the tunnels for steam.

* The carriages will be used on all four sub-surface lines with platform
lengthenings where necessary (and presumably also track variations). As well
as the possibility of formal line rearrangements (e.g. Met to Barking and
turning the rest of the H&C and Circle into a Tea-Cup) this also makes it
easier to run special services, particularly to bypass engineering works.
(How likely is a Wimbledon to Barking via Baker Street through service when
the Embankment route is out of action?) However it could create problems for
the Chesham shuttle service - the bay road at Chalfont & Latimer is too
short for a full-length train (as would be a restored bay at Chesham) and
the station prevents expansion.

(Come to think of it isn't one of the latest timetable proposals aiming to
replace the shuttle service with through trains diverted from Amersham?)