One thing which I think might be a nice feature is that once you've closed a line into an object, I'd like to be able to pick it up and move it around like I can with railway tracks.

It would be great to be able to do that so that one can build the object away from the track, set it to the right dimensions using the rulers and then move it to the best location.

Indeed, all of that would make creating the cities etc all that much easier and more feasible!
Hopefully it wouldn't be too difficult to get it integrated into the software.