My Suggestion for train as part of a future DLC or just the train as add on would be the Class 325. The Class 325 are 16 car units build between 1995 and 1996 and were build for mail services. It picks up energy from both an Pantograph (AC) and a Contact shoe (DC) . It operates between London, Warrington and Glasgow on the West Coast Main Line. There is also an additional service between Willesden and Low Fell on the East Coast Main Line. I personally think it would be a great addition to the game as its kind of a specia freight train and one of my favourite freight trains on the british network. Hope this is a good suggestion!
Just needs either West Coast or east coast main line because they are actually designed to run postal mail services on both routes. For train simulator world 2 the same people that worked it for sister game train Sim 21 must be brought back to work on it for train simulator world 2.