Hi David, nice to meet you
I don't do much AutoLisp and I haven't read your book/s but if you want to write something different I think there's plenty of scope for a 'what's next' type book.
That is, how to set up a larger projects, how to format your code, testing and other best practices. Maybe even things like writing lower level functions in C#/C++.
It's pretty easy to hack together some routines but pretty soon everyone hits that wall of spaghetti code but if you start off with a good strategy things are easier to maintain and extend.
Maybe it can be part of a rehash or a book in itself?
Either way, best of luck, cheers.
Mick