A good read. One of the more interesting, informative and well written pieces to appear here in a while.

The one concern I have with this playbook is that fashions in niche technical subjects change (I think) very quickly. For this to beat simply selling coding services on a T+M basis the revenue stream would need to continue for several years, with a suite of similar books/courses added over time. Are people still going to be interested in paying money to learn about Ruby performance in 2 years from now? Can two, three, four equally profitable subject be identified and mined every year? Probably not, unfortunately, due to this industry's eternal desire to churn the tech (often to no obvious positive purpose).