Hi I think Bristol Temple Meads to Westbury would be a nice addition to the game. It offers the chance to run local stopper services and semi fast services. There is also a wide variety of freight that runs along the line. For possible traction to use the class 166 could be used along with the HST and 66 for the freight and the 08 in Westbury yard. Other trains that run along the line include the class 150, 153 and 158 for the whole length so maybe the 158 could be included with the pack with the 150 being a potential DLC. I have seen a lot of Colas Class 70s run along the line aswell so that could be a potential freight DLC.
The class 153 doesn't actually run along this line anymore, they were moved to Cornwall when the 166s moved down from London, I think this rout would be a great addition, although I think Westbury to Weymouth would be better, Idealy Bristol TM to Weymouth would be the best