Maybe, for scenarios on the East Coastway, they could add that train for a new scenario called 'London Bound Diversions'. There is works between Brighton and Burgers Hill so all trains are diverted via Lewes and Eastbourne and then go back to Lewes on P2. The train you got to drive is a Gatwick Express 387 formed of 12 coaches! Hope you enjoy! Also, maybe don't add this train into timetable mode but put the train into Scenario Maker
Now that we have scenario mode, they could just make separate trains (not connected to any route in particular) for us to use. Of course they can charge money for the trains, but it’d be nice to get a catalogue of choice.
Diversions via Lewes typically turn back at a signal just round the corner from Lewes box. They don't go to Eastbourne. But it is definately a shame they didn't include Cooksbridge and plumpton, it would have been nice to taken the 66 a bit further. And like you say, a Brighton diversion.
They are still running down to Eastbourne on the 1GXX devices though. During COVID and the Gatwick upgrades