Custom path creation. I mean think about it. If Nolimits 2 made a better attempt at what TPS tried to do, the ideas could be unlimited.
Think of it like this, a tab for path creation, with maybe 3 different paths to choose from. You can also make your own 3D paths and hook it up to the tool, similar to how track is made, you would just add nodes for the paths, and you can connect nodes to preset pieces that can merge or split paths into two. In other words, you can also connect stairs to nodes and buildings etc. With enough thought it would be a fairly simple addition to the game and could do wonders