Well now the announcement of the "Holiday Express" DLC has been confirmed as a round the room style model railway, we have proof of concept this type of route is possible in TSW. So I would like to suggest an ongoing offshoot project - Model Train Sim World or Great Model Railways to capture and allow us to explore some of the great layouts that have appeared in plan books or built over the years. Off the top of my head I can think of several... Pendon Museum Mevagissey Model Railway Buckingham Great Central Any of the many Peco track plans especially the larger layouts. Moth Lake & Mount Ahab Hungry Horse Sierra Pacific layout of the Pasadena Model Railroad Museum The list could be endless. All subject to licencing of course.
The two that I would love to see would be the Miniature Wonderland layout in Hamburg, Germany, and the Chicago Museum of Science and Industry layout which depicts the tracks between Chicago and Seattle. My last idea is Tony Lash's O-Scale layout (which is pretty impressive).
I’m sure this would be complex to do for real, but could you imagine the ability to set up one’s own set track following a manufacturer’s geometry as a layout planner in TSW. Basic flattish scenery assets already in situ to create an easy use environment. No need for it to be a more full on editor. It would work wonders for those of us who’d love to build a model railway but unsure of their plans, or even for folk who don’t have room for one in reality.
You might already be aware but there is some software out there for layout planning (like SCARM is one though I haven't used any myself so if interested look/ask around first) on your computer. Some do 3D models others are more top down visual. But I definitely wouldn't mind seeing something like you described happen in TSW.