Writing a book when you don't know the subject matter doesn't sound likely to result in a good book. Even more so for a language like Rust, which (short of Haskell) is the closest thing to a mainstream language that is informed by a lot of pointy headed PL (programming language) theory. A book about programming in Rust doesn't have to go into the theory per se, but the author should be familiar with it, just like someone who writes an introductory calculus or statistics text really needs a much deeper mathematical background than the book itself will convey.

If you want a Rust-related hobby, first of all, why not do Advent of Code in Rust, or otherwise make a study of Rust? And then if you're interested in PL theory, that's another area to study. Harper's book PFPL is a good place to start: https://www.cs.cmu.edu/~rwh/pfpl/