I think it even is possible with no changes to the code - just make some more impassable terrain like the sea.
It'd be nice to slow down worldmap speed, and introduce more mass transit systems. You can walk to the neighbouring towns, but if you want to cross the wasteland you better get a train or hitch a ride with a caravan.
Problem is, that height and cliffs, etc. are already simulated with travel speed differences (high / low terrain). Everything else (except rivers) is hardly possible to realize in a good and realistic way.