I really like the idea of a more content-based approach to book discovery. It feels like a complex problem to me, since there are so many dimensions one could pivot on; and how to find them in the first place? As an example, I dislike first-person books even if they might seem like really good fits for the kinds of topics I read. There's also a clustering issue around "well, I like sappy space opera when I'm on vacation but more cerebral fantasy epics on the train". But good luck with solving that.