I have thought this for ages. When you complete all the maps, then its either just drive around ( which I have done for hours and do enjoy it) or redo the maps. If you ran a logging company would give purpose to playing a map for years, which I really want to do.
Game is not yet out, and you want to implement such hard thing. Trust me, there will be more maps even larger and difficult, even challenge mode. I agree with you, wish to see more content or dlc which will prolong game experience further.