Power supply needs to be upgraded at Marshall meadows before additional services can be introduced. That’s one of many reasons why the scotrail service terminates at Dunbar and TPE are diesel powered.
An Edinburgh newcastle stopper would have a market, and Reston and east Linton help justify it as well as increasing services from chathill onwards. Problem is track capacity and little if any opportunity for stoppers to be passed by Express LNER TPE and XC services. Those few loops already in place are usually occupied by freight when the 3 intercity services pass
Looks like there are Up & Down sidings at Reston, wonder if they could be turned into loops?