I'm writing a book on building and launching mobile apps end-to-end ( https://opinionatedlaunch.com ). I'm treating it like building and launching an app (Dogfooding my method! But for book-writing!). It's got a website, a marketing plan, and even an affiliate system.

I took the self-publishing route because the book's target market is niche; there's only one CTO in a company. Someone I know went the publisher route, and I think he's quite successful. I have only sold a dozen so far, but I'm pricing it accordingly.

In summary, I like to think of book authoring as starting a SaaS. Start from your target market, then the book topic, then from there you can tell whether you can cast a wide net, or aim narrowly.