How will that work?
Seaford is single track, are they really going to have an empty train blocking up Seaford Station for most of a Saturday afternoon?
If they're going to park it somewhere down there, surely Newhaven Marine or whatever that thing is called is the only choice.
They won't leave it at Seaford. The branch is signalled as "only one train at a time" beyond Newhaven Harbour. Newhaven Marine is effectively closed off.
Although the Brighton to Lewes line may be signalled as bi-directional on both lines, it would only be operated like that in an emergency. You wouldn't have two trains shuttling up and down on sparate lines, be far too confusing for all the platform announcement machines.
The whole planning permission for the Falmer stadium was based on the fact that Southern would run a shuttle between Brighton, where there are usually spare platforms on Saturday on the East side, and Lewes, where there is a bay platform on the South side. I assumed that trains would be turned around at Lewes.
The reason for including this in the planning permission was it cut down on the need for huge car-parking space at Falmer, which was not available with the present site, only the coach-park on the east (LDC-controlled) side.