Sure, but intrasystem travel will only be economical if we can mine and get fuel, energy, and mass from non-Earth sources. If we get to that point, scaling up

Sure, but intrasystem travel will only be economical if we can mine and get fuel, energy, and mass from non-Earth sources. If we get to that point, scaling up just consists of waiting a few decades of exponential growth to kick in. It might not even involve humans, but just letting automated robots continue to build more robots. If the technology is there, moving mountains instead of ships is just a small jump.