I have just bought Transport Giant and watching the two little guys build my tracks, I had an idea for Train Fever. It would be cool to select a route for my trains from point A to point B. I would set some parameters such as minimum degree of curvature and maximum grade for my line. Then the game would send out surveyors, graders, and eventually track layers (picks and shovels in the early days and modern track laying machines in the present) and I can watch the realistic building of my line.
Maybe the surveyors will come up with some optional routes (longer but low grade, steeper so more horsepower required, shorter but needs an expensive tunnel, etc.), and I would have to chose the one I want.
It maybe something that is not that important, but I would enjoy watching the detailed building of my lines like I watch the building of the buildings in Sim City. It would just be a cool feature.