The cost has already been paid. Even small farming communities have rail line access that's mostly been abandoned because the line owners switched business models.

As for flexibility, again, that's mostly an issue with how rail line management has evolved. From shorter more frequent trains to ultra long infrequent trains. Mostly to cut the cost of staffing.

The solution is simple, nationalize the rail service. Put it under the USPS and have them figure out scheduling to optimize the speed of goods shipping.

The current state of the rail system is entirely due to the monopolistic nature of ownership. The incentive is to increase prices as much as possible while shipping to the fewest stops possible. Profit motives are in direct conflict with generalized shipping.

The reason trunking works today is the public nature of roads. Well, why shouldn't rail lines be equally public? We practically gave the property away to the current rail owners with the notion it was for the public good... They've failed that.