Since the new Coastway route is coming out, a 313 would be nice. Southern livery, maybe even BR Blue 313201. All the standard features (like those in the AP 313/2 and the standard TSW stuff). Operating mostly 3 car formation. Not sure where depot(s) will be but maybe involve a move to or from Lover’s Walk as a 6 car.
I only dream of 313s coming as an addon to the costway dlc. But it seems highly likely that they will add it because the are very common in the Brighton, Seaford line in real life.