Building paved areas (central twon squares/piazzas)

[Grautvornix]

Just saw this beautiful screenshots by @wowgetoffyourcellphone showing a roman city built around a central paved town square/piazza:

The game is rightfully famous for many things - but also for allowing to build beautiful scenarios. Just, if you happen to not use the ATLAS map/scenario editor, how can you build your city around a paved area?

Many maps already provide such an area from the beginning, but you need a lot of planning ahead in order to allow sufficient space for builduings that can only be build in a later phase (temple, wonder etc.). 

Would it be possible at all to allow building a kind of paved area during the game? The typical issue would remain that it needs to be an object that can be crossed also by the pathfinding algorithm. As such it needs to be a building that, while visible, is not blocking and acts rather as a decal with a specific aura (e.g. market features, agora/politics, negative aura for files/reduced soil fertility). Upgrades from sand to gravel to cobblestone would increase the strength or range of the aura.

If such thing can be implemented, it could open other interesting possibilities as well: building roads (movement speed), bridges (can be crossed by land forces but not by ships, can be destroyed by ships), channels (can be crossed by ships but not by land forces). Also we could designate/build areas of fertility/watered areas if the respective technology was invented. For each there could be technology steps (wooden bridge, up to stone bridge, farm lane to planked path to paved road etc.)

Just dreaming a bit ....