What a lot of concepts ignore is material requirements, which is super-important. A good example is Larry Niven's Ringworld. It's a cool idea in the early days

What a lot of concepts ignore is material requirements, which is super-important. A good example is Larry Niven's Ringworld. It's a cool idea in the early days when people were thinking about mass-to-living-area ratio but to produce Earth-like gravity at an Earth-like distance would require the thing to spin at (IIRC) ~1.5m km/h. The centrifugal force would tear that apart. Likewise, people mistakenly view a Dyson Sphere as a rigid shell around a star. That was never the concept. This misconception is so common it's led to the term Dyson Swarm, which was always the original intent: a "cloud" of orbitals around a star all moving independently. The likely future of space habitation is (IMHO) going to use the humble O'Neil Cylinder [1]. This is nothing more than a cylinder a few miles wide and maybe a couple of dozen long. Such a cylinder could potentially house millions. They're large enough such that spin gravity wouldn't be disorienting and small enough such that they don't require exotic materials (eg space elevators for Earth require exotic materials we haven't even theorized yet other than possibly graphene). So an O'Neil cylinder can be built of nothing more sophisticated than stainless steel. You have options of joining them to other cylinders. You can build a "ladder", which is a series of orbitals all in the same orbit but slightly displaced. You could even run cables for transportation between them. You could construct networks of these things. You put solar cells on the outside and a window at one end, possibly using refractive materials down the center to create more pleasing diffuse light and the whole thing is reasonably low tech and low maintenance. You could even build them by hollowing out asteroids and other space bodies. The mac daddy to the O'Neil Cylinder is the McKendree Cylinder [2]. Instead of being a few miles wide, it might be hundreds of miles wide and much longer. This is beyond the tensile strength of stainless steel but within the theorized limits of graphene. Such a cylinder could comfortably house billions of people. As much as it's cool to have things like the micro-gee environment of the ISS, I honestly wish we'd start building prototypes for spin gravity. This would greatly simplify living in such an environment for extended period of time. To give you an idea of how efficient thing is for living area, IIRC the estimate is about 1% of the mass of Mercury could consume essentially be a complete Dyson Swarm around the Sun and comfortably house a quintillion (10^15) people. Planets are nice and all but are horribly inefficient uses of mass to create living area and come with some serious negatives, not the least of which is the energy cost of entering and leaving such a gravity well. This is also why looking for the signature of such a Dyson Swarm as evidence of extraterrestrial spacefaring life makes way more sense than pretty much any other approach. Saying that we're less than 1000 years away from having this kind of space-industry is beyond conservative. 1000 years ago we were throwing spears at each other. [1]: https://en.wikipedia.org/wiki/O%27Neill_cylinder https://en.wikipedia.org/wiki/O%27Neill_cylinder [2]: https://en.wikipedia.org/wiki/McKendree_cylinder https://en.wikipedia.org/wiki/McKendree_cylinder