You did not say if your book would be about Japanese weapons much like what's available from Don Cunningham at www.e-budostore.com
or an Aikido weapons book like Gaku Homma's "The Structure of Aikido
One area I am interested in would be to learn the history and evolution of the AIkido weapon systems used by Saotome (ASU), Saito (Iwama), Shirata (John Stevens), etc. and perhaps to take that deeper and to look at o sensei's weapons background and from that what he chose to incorporate into Aikido.
On the technical side of things I'd be more interested in learning about "why" we do certain things than "how" to do them. There is a "why" behind each of the subiru, kumi tachi, kumi jo, kata, etc.
Good luck and best wishes on your book project.