Maester Steven, may I please ask if your Economic Development Plans would be subject to alteration were they applied to now defunct polities like the Kingdom of the Storm (in its “Sea to Shining Sea” phase) or the Ironborn domains during those years of darkness when the Islanders writ ran from the Arbor to Bear Islands?

Oh definitely they would change. As with Jaehaerys and his roads, economic and infrastructure development is usually driven by the interests of the center over the periphery. 

So to take your example, I would imagine the Durrandons would discourage a Blue Fork canal in favor of a canal linking the Godseye to the Trident, as that would facilitate traffic in a southerly direction closer to the “home territories.”

As for the Ironborn at their coastal peak, well, they were rather notoriously uninterested in infrastructure that didn’t have to do with longships. Indeed, I would imagine they would ban bridge-building as a potential check on their power. But in the Hoare era of rulership over the Riverlands, I could see them favoring a Blue Fork canal to give the Iron Islands direct access to the Narrow Sea.