Outside of large cities, most of America can't even afford the upkeep associated with their existing infrastructure. I'm not sure how you think they'll be able to afford large scale fiber deployments.
Or maybe you're saying that private ISPs will perform the deployment and then share their fiber? Which seems wildly unrealistic.
Rural flat areas: I expect fixed point wireless to be more prevalent.
firms specialize, it's an important attribute of a functioning free market. If there is demand for running fiber through conduits, local firms might specialize in that type of construction, especially if local knowledge and working with local governments can be leveraged across customers. Many industries are not vertically integrated where specialization is more efficient than vertical integration. (i.e. Ford stopped making tires and glass)
Or maybe you're saying that private ISPs will perform the deployment and then share their fiber? Which seems wildly unrealistic.