For info, I'm currently finishing off my third book, this one on Astrophotography, to be published by Focal Press in the new year. The initial reviewers of the book proposal all asked for PI content.
It includes over 100 pages on PI processing, including an introduction, alternative PI workflows and how to use it on a number of example images and comparing it with other applications' tools. To achieve this I have had to evaluate and make sense of dozens of resources on web and forum and then consolidate this into a structured approach. The research and writing has propelled my learning and I'm glad they demanded it.
100 pages is not enough though - it deserves many more to fully do PI justice.
Maybe there is a collaborative project out there - between the developers and the users, to put something back to the community?
regards
Chris Woodhouse