It would be great! I think there is no Backbone.js book in the market right now.
Have you looked at Addy Osmani’s books: http://addyosmani.com/blog/backbone-fundamentals/ and http://addyosmani.github.io/backbone-fundamentals/ ?
What type of content would you want to be covered? I’m writing a book on a related subject (Marionette.js, which enhances Backbone), so I’d be interested to know what you’d exepct to find in a book.
My planned content outline can be found at https://leanpub.com/marionette-gentle-introduction and I’d love feedback on subjects that might be missing.