It looks great. I have not read it to completion just yet, but merely scrolling through the document leaves me with a feeling that the author got tired and decided "this is a good stopping point."

To be fair, writing a book about Emacs is a Sisyphean effort by definition - this sea is a bottomless abyss of hackery abundance, and any meaningful effort to explain it is worth a celebration.

The Emacs' bundled documentation on Elisp (both the intro and the rest) are pretty much complete enough.

On Elisp and multithreading/processing, well, just look at bordeaux-threads in Common Lisp where the support is not universal for Clisp. SBCL and ECL work, but...

I have a silly little vibe coded extension where I can star certain HN commenters so I know who to look for in which threads (just puts a small symbol next to the username)

You are for emacs, happy to see you here... :)