My impression is the boring feasibility and costs will not be the limiter of a very cool tech like this happening, but a more boring practical cost, probably the "zoning" cost required to get compliance and permission for all that state and federal land needed to build the underground link network.
[1] http://www.sheepletv.com/nuclear-tunnel-boring-machines-swit... [2] https://en.wikipedia.org/wiki/Subterrene
My impression is the boring feasibility and costs will not be the limiter of a very cool tech like this happening, but a more boring practical cost, probably the "zoning" cost required to get compliance and permission for all that state and federal land needed to build the underground link network.