I've recently been contacted by a number of publishers that are actively looking for Drupal book authors. Packt Publishing sent me such a request today. They would like to hear from Drupal users any Drupal book ideas they may have and would like to see published, even if a proposed book caters for the needs of a smaller section of the Drupal community. They are also interested in hearing from any Drupal user who is interested in writing about Drupal, whether they have a specific book idea or not. If you have a book idea or if you are interested in writing about Drupal, let me know in the comments, and I'll introduce you to the right people.
The cool thing about Packt Publishing is that they have a lucrative Open Source Project Royalty scheme. From all the Drupal books published to date, the one from Packt Publishing generated the most royalties for the Drupal Association. That alone gives me sufficient reason to publish their call for Drupal book ideas and Drupal book authors.