The Thameslink service will terminate at Cambridge using the bay platforms that are currently used by Greater Anglia. This is because the Greater Anglian new fleet won't fit in the bay platforms.
Whether all this was known at the time who knows.
Thank you. That is new to me but almost certainly true. The Cambridge bays won't take 12 (x20m equivalent) coaches.
12 coach trains are a problem at Cambridge. Platforms 7 and 8 take 12s with no issues. I think platform 1 takes 12 coaches but not 387s southbound because the gangway obscures the driver's view of the signal. I don't think platform 4 takes 12 coaches. The Brightons are always 12s and a significant number of King's Cross fasts as well which couple in the platform to make matters worse.
Looking at the planned service after the timetable change on realtimetrains, there are a few GA trains using the south end bays early in the morning so they could be diagrammed for a single set. During the day, the Thameslink slows monopolise the platforms 2 and 3 as they have long layovers.
There are issues elsewhere on the GA network with those trains as well which suggests that no one in the bid team thought it through before putting them in the bid (like the Brantham depot)
The new GA trains will be 5 car or 10 car but the coaches are longer - effectively equivalent to 6 x20m and 12 x 20m in total length.