as a beginner, but fascinated with spey and dee flies, and starting to learn full dress, I am interested in "light" reading on how to dye feathers and all that other stuff, I read Michael R's section on hook making with interest but I am not there yet. I think a nice chapter on how they used to dye, couple that with modern methods to create the same effect would be very interesting reading. Since your book seems to be taking on a historical flair, you should include those. Would be interesting because many of the "Newer" books on the shelves are "Modern techniques" type books.
Sorry for the ramblings, just thinking while writing