[Wormius]

This makes me wonder about what would be the problem of using metal grates for roads rather than standard paving.

Pros: no potholes, easily replaced, no pooling of water.
Cons: cost, slippery, durability?

Anyway, despite the cost prohibitive nature of the roads suggested in the OP's post, they should be encouraged, even if just on a trial basis. Can always learn something from it.

edit: that sounded crazy when written out.