> most of the C code by volume is things that could perfectly well be implemented in Emacs Lisp itself, A substantial part of the GNU Emacs core is written in

> most of the C code by volume is things that could perfectly well be implemented in Emacs Lisp itself, A substantial part of the GNU Emacs core is written in C: the byte code virtual machine, the core Emacs Lisp language implementation, loading/saving images, memory management, ... That's not implementable in the current Lisp architecture (which additionally is single threaded). If we want to move more of the language implementation in Lisp, that's possible - see implementations like SBCL or Clozure CL. Porting/maintaining these seems more difficult. But then you can implement regexes and other stuff in Lisp.