Next-Generation variable-buoyancy airships, without a doubt. Primarily because of the ways it will impact construction. Once we 'build the machine that builds t

Next-Generation variable-buoyancy airships, without a doubt. Primarily because of the ways it will impact construction. Once we 'build the machine that builds the buildings' we can then simply lift them into place. Cities could become vastly more flexible (modular) and livable as a result. But even agriculture and logging could become vastly less environmentally destructive.