I'm curious to know what people think about elisp as a extension language. Would Emacs be better if everything was implemented in elisp including the core data structures (assuming elisp was very fast)? Do people suffer from lack of static typing?
Elisp is nowhere near perfect, but it's fast enough in general. I recently wrote an indent function for a private DSL; it looks like a big slow mess, but when I run it on a code file, it does its job with no noticeable lag. You can write slow code in any language, of course.