It depends how the original proposal is interpreted. This was debated elsewhere regarding SWT a couple of years back, when people were racking their brains trying to work out how to extend all the 455 operated services to ten car - clearly this would require about 91 carriage equivalents, to go with the existing 91 four car units.
But then an SWT driver chipped in with the point that it didn't need to be throughout the peak, just the high peak, and careful diagramming would ensure that most arrivals between 8 and 9 could be 10 car.
Now in the SN case, which of the following do they really mean?
a. every train on all those routes will be ten car,
b. some of the trains on all routes,
c. all of the trains on some of the routes
d. some of the trains on some of the routes...