When I read the title I thought of another IDEA that I've had bumping around in my head that would be pretty cool.

Put down two model railroad straightaways next to each other, with two locomotives, use them as a base to attach a 3d-printer arm across and "print" a model railroad diorama, incrementally moving the locomotives to print each slice.

In other words, a flatbed 3d printer where one axis is the locomotives moving across your railroad layout. I think it could rejuvenate model railroads if you could print mountains, towns, streambeds, roads, etc...