One of the (few) features I actually liked from City Life (the predecessor to Cities XL) is that it allowed you to expand your city buy purchasing surrounding parcels of land. You would be contrained to a square tile, however each section of land you could buy was not necessarily square. As you needed more land (and you could afford to buy more land) you could expand the size of your city.
This is a feature that would be cool to have in SC2013. While it won't happen since development is so far now, we can always dream, can't we? What do you think of this idea - especially given the relatively small city tile size in SC2013?