IMO, 1 million people is not enough to make a self-sustennable colony on Mars, because it'll need to reproduce a whole industrial system to maintain itself. Perhaps with AI and robots it could be done, but will AI and robots be sufficiently advanced in 35 years to maintain themselves, and go mining and milling and repairing themselves and building their replacement, let alone doing all that is needed to sustain the life of 1 million people, even with their help? And how does this makes SpaceX a $trillion company?
IMO the real 4- and 5-comma companies won't be the companies that will take stuff off Earth, and probably not companies that will bring stuff from space down to Earth (because this market will be the limited Earth market, which is billion-sized). No, it will come from companies that will take raw stuff from space, and refine it and produce end-products in space, notably big stuff, like big space ships, and space-stations (habitats). Eventually they will compete with all industry and agriculture on Earth, and eat that market, but it will be but a drop in the ocean of the market in space. And their valuation will be automatically in the 4-comma, because of the cost to bring stuff to LEO from Earth, if we had to do it, even if Elon could bring the cost of that to very cheap. (give the mass of a space habitat, or of space farms able to feed the Earthlings and the Spacemen).
But people at SpaceX are smart, they're already doing money "in-space" (with the StarLink satellites), and they'll be sufficiently advanced to be amongst the first companies to fork pure space companies. And with headquarters on Mars, they won't have to pay taxes to Earth ;-)