An idea that came to mind because I'm a huge fan of the whole exploreing abandoned places especially thoes with locomotives and carriges left behind for good. So why not re-create this experience in TSW, because TSW has achived in my eyes the perfect scenery experience which I've seen myself while exploring the routes on foot. I would love to experience exploring abandoned rail tunnells, or areas in the woods or where ever i'd be a good spot to dump some old locos and carriges and get up close with them, still interact with them and so on on but the only thing you can't do is drive them away. The enviroment objects will still allow you to sit down, open windows, close and open doors, climb up the carriges and walk around. Maybe turn on the power but highly doubt it will move. A very nice idea if you ask me.
Nice idea, but TrainSim devs have stated that they will not make weathered rolling stock in order to preserve the image of them and the company they are modelling. Because of this, I only see this as being possible if it was a 3rd party project.