The game's landscape - what are the limits?

[Lagarto]

The continuous development of this sim (thanks for that) makes me wonder what are the limits of the game's decade-old engine. Surely some things cannot be done, or can they?
Like, for example, new maps featuring double-lane roads and railway tracks, railway embankments (a common feature of European landscape, as seen in many guncamera clips), navigable rivers, and first and foremost, roads running in a more natural, curvy way, not this odd-looking zigzagging?