For the most part I followed this. Some of it I didn’t. Can you explain what you mean by lateral offset?
's some information that might help a bit with elaborating more on my idea. Both wheel trucks would look at the dummy object, that way both have the same rotation value. Also I know that not all curves stay at the same angle, but that would be fixed with the modular track idea. You would have a selection of track pieces (all based on realistic radius’s/angles) that you can then piece together to get what you want. It would allow far more customization depending on what you need for your game map.
For most transition problems, you could just set some sort of smoothing to the transition between rail pieces (probably based on the distance between the dummy objects for each piece of track), that way the wheel trucks should transition smoothly between a straight piece to a curve piece to another curve (or straight piece).
And I think as long as the dummy objects can be used, the wheel trucks shouldn’t have issues with taking a curve and still looking believable. As they are looking at a rotation value that would continue through the curved piece of track and as long as the train can follow along the track (and not just a single axis), then I feel like this idea/method would be a good alternative.