One thing I thought would be enjoyable, and enable a quicker turnaround would be reusing the same route, but setting it in different eras. The thing that stopped me buying Diesel Legends of the Great Western was that the 1970's era trains look out of place on a 2010's line out of a clean and modern Paddington, with modern buildings, stations, cars, etc. Reusing the routes, elements of scenery, and appropriate assets would make a world of difference to the immersiveness. I would love to play that route, and others, with rolling stock and buildings as they were at the time (or doing an old route as it is now - Trans Pennine as it is today would be fantastic), as would a 1970's version of the GWML.
