The core of it is described by the post you're replying to as "I imagine an LLM would be very good at writing Elisp to leverage EMacs’ strong core functionality to make Emacs work exactly how you want."

Emacs is highly customisable. There's not really a hard difference between "configuration" and "extension". Whereas with e.g. VSCode, very few people would write their own extensions. -- So it's a good point that with LLMs, the barrier to customise Emacs to exactly how you want it is even lower.

I'd also argue that since practically everything in Emacs is text (as opposed to a rich GUI interface), Emacs itself ought to make for a nice interface to LLM functionality.