This sounds really great and I think it's something the SFML community has been waiting for quite a while.
As a matter of fact I amplaning on working on a set of tutorials which would slowly progress in difficulty and complexity and which should empower readers to create their own nice game at the end. When you have such a thing in mind the idea of publishing the tutorials in book-form isn't that far away and seeing that topic here now, seems like a very interesting coincidence.
BUT as much as I like to write down and pass on knowledge, I somehow don't feel like that I'm best suited for this task. Since my native language is not English, I make quite a lot of mistakes and to me the whole phrasing seems often to be repetitive and artificial. Furthermore my knowledge on SFML doesn't go into all modules, e.g. I've nearly no idea how to work with the networking part and have never really experimented with the audio module. And then there are the usual factor like time, etc...
I'd gladly team up with someone or contribute in other ways to such a book, but don't see me as
the author of the very first official SFML book.
That said I'm probably gonna keep working on my tutorials (for now), which don't require to be as correct and nicely written as a book and if someone wants to team up, I'd be here to help out.