Okay. Lack of imagination on my part: I was primed to imagine a Dyson Sphere built around the solar system, not a small, pre-mercurial, partial structure. After all, inconcievable doesn't mean impossible.

Nevertheless, I want to portray a humanity that's focused on conservation and optimization and recycling and re-using. At least as an intermediate step before attempting to tame the Solar System. Even when they move out, I want them to be sustainable in terms of resources in the scale of billions of years. Meaning that the regime that we're keeping right now (humans have moved and processed so much rock, we're a geological era all by ourselves) wouldn't be the one we'd be using in The Future.