I am in complete agreement with this.
After creating roads and bridges and railroad tracks.
It would be a lot easier and more optimized if I could export the terrain then draw a 3d polyline across the spots I would like the roads and rails roads to go, then do a loft of the road or rail road profile to have a perfect match to the terrain.
The is a lot of editing that you can do in terrain edit mode, but having the terrain exported, would allow you to make better models that perfectly match the terrain.