There are plenty of Amiga programming books available second hand and some new, such as the series published by Abacus. They tend to concentrate a lot on things like intuition, system devices, etc.
What I think would be most useful in a new book would be to focus on things like ReAction and MUI programming. There's very little, if any, printed books covering those aspects of GUI programming.
I know of quite a number of programmers who would be keen on something like that, myself included.
