We'd prefer not to depend on node.js and the gitbook infrastructure. It should be pretty easy to wrap or extend rustdoc with support for the basic gitbook features used by the guidelines.
Maybe talk to the guys over at https://github.com/japaric/rust-by-example, who knows maybe a consistent shell could be made.
I've written a tiny version of gitbook in Rust: rustbook, which works on top of rustdoc (and thus uses the same styling, syntax, etc.) For now, the tool only allows you to render the book, but I plan to add testing soon.