The article is adapted from Musk's presentation at the International Astronautical Congress and begins with an argument for why we should focus on Mars for our move towards interplanetary life. Musk then notes that with current technologies, a ticket to Mars would cost around $10 billion, which he correctly deduces is a prohibitive amount if we want to actually colonize another planet.
Getting that cost down to the median price of a house -- around $200,000 -- is key to making the Mars plan viable, says Musk. And he outlines four essential steps that will need to be taken if there's any hope of doing that. First, the transportation would have to be fully reusable because any amount of waste would significantly increase the cost. And ships would need to be refilled while in orbit. Additionally, we would need to be able to produce propellant on Mars and it would have to be optimized for cost, reusability, and easy production -- Musk proposes methane.
Musk then proceeds to detail the proposed engine, rocket booster and ship as well as how many ships we would need and how many people each one should be able to carry. For the crew compartment Musk says, "There will be movies, lecture halls, cabins, and a restaurant. It will be really fun to go. You are going to have a great time!"
Musk sketches a rough timeline for these events, but keeps it purposefully vague. It's clear, however, that this is something he's actively working towards. The fifteen-page journal article is not quite what you expect to see in a peer-reviewed journal -- there are some humorously unnecessary venn diagrams and a few tables that are nothing more than bullet points. But it's a much more flushed out write-up than we usually get from Musk. To see the presentation the article is based on, check out the video below.