Oh it's nowhere near halfway there. I think the idea of using git is a fine one, but some software engineering is very much required. Ideally the project would work for all phases including pushing updated copies to consumers. Once you think in those terms you start approaching a product that's going to work for non technical editors and writers.

A customized book reading application that allow critical readers to make marginal notes and corrections, and see and rate other people's marginal notes and corrections would be the ticket.