Let weeds and grasses be able to grow up through the rails, that way if a train hasn't gone through in a while the tracks will be overgrown(trains would destroy things growing through the rails like they do snow blocks). Additionally, some really poorly maintained trackage like THESE TRACKS HERE be great once derailment is a thing. These bad tracks should have a good chance of derailing you if you take locomotives/cars on them that are too heavy or if you attempt to go too fast over them.

I hope rails requiring maintenance will be a config option - keeping up with that might not be too hard in cooperative multiplayer, but in singleplayer it could easily get out of hand quickly.