I'm a huge fan of the South Devon Main Line + Riviera Line in the Fifties and the Preußische Ostbahn, but that might have to do with the fact I suggested them . Something from the American Post-War steam glory days would also be great, like an SP daylight route that also features cab-forwards, or a PRR route.
I'd take something like the Mallard or Flying Scotsman on the ECML, however I'd much, much prefer the ECML to be mostly modern (Late BR- Present). Same for Settle - Carlisle, but with a Sprinter for that variety (like the TS Version) I would, however, take both of the routes suggested by jolojonasgames in a flash. They're both brilliant.
I would like to see a few standard British workhorses represented. Special and particular locos are great, but for creating an immersive timetable we’d need decent run of the mill stock to flesh it all out.
If you want a German Steam railway action combined with Mainline tour perhaps Bochum Dahlhausen steam railway will fit because it's connected to Hauptstrecke Rhein-Ruhr Essen branch S-Bahn line S3. Most of their steam locomotives are former Deutsche Bundesbahn 001-099 class.
I assume they would start with a small steam shunter to test the systems modelling before attempting a more complicated mainline locomotive. Perhaps an add-on for the West Somerset, rather than a Pennsylvanian T1. (one day if we’re lucky)
