the one thing that would potentially be useful at Stratford International (and one of several factors that's stopped it being used a "budget" terminal) would be a reversing siding to the west of the station, so that you could have a train arrive on 1, empty, shunt into the reversing siding and then either go to the depot, or into platform 4 to start a service.
Reversing WAS considered for the domestic services, Stratford International East Junction crossover allows trains to use either domestic platform when arriving from and departing towards the east. Any such reversing siding would however be underneath the River Lea and the Lee Navigation