I noticed the same today on the way back from Edinburgh, I didn't even know those platforms were there. They'd be useful for terminating trains via the Northumberland line.
The north facing bay platform is currently underneath the car park.
If the de-vegetation work is taking place around the back of the down platform, number 2, then that used to be a loop line. There was briefly a platform face on that loop, and it would be very well used to get the Morpeth terminators out of the way of the ECML if a reverse crossover south of the station were to allow it; having the unit turn around in a bay platform would save a ten minute reverse in times of disruption, and would allow longer units to run.
The problem however is that platform 2 currently extends to the edge of the bridge over Shields Road, and you'd need another span adjacent to give you enough room for an extra platform.
Incidentally, this is all immaterial anyway, such a platform would be helpful if it were facing south, facing north it would be impossible to run on to the Northumberland line at Bedlington. The points to access the Northumberland line are halfway along platform two, and any bay platform around the back of platform two wouldn't link up.
