In keeping with the philosophy of being hands on; would the book be improved if after introducing the code in the first section, have the reader implement an exploit for the same code?
I do not feel remotely comfortable with the idea of writing a book containing prescriptions on how to design a cryptosystem. We're wary of doing that even for our clients, where we know all of the context and the threat model that the proposed system would face, and who will actually build it, and that we'll get paid to review the resulting implementation. I don't know how to solve that problem for strangers.
Other people do. They are much better than I am. When Trevor and Moxie write the book on why they chose the TextSecure primitives that they chose, I'll be first in line to buy.
You know, for old times' sake?