OK I admit that the distance may make one whole route an impossibility but I'd love to see either a Birmingham New Street to Leicester DLC or Leicester to Peterborough DLC, Either set in the 1980s or 1990s. Class 31s, 47s, first and second generation DMU, Passenger and freight stock. Could be fun.
Leicester to Peterborough would be doable, given neither are particularly loaded with different stock With class 156 EMR and 170 XC you could populate the route pretty well, with a 66 layer for freight. Route length is just over 52 miles, with stops at Syston, Melton Mowbray, Oakham, Stamford and Peterborough