Bringing GNU Emacs to native code [video]

That's already been done. More than once, in fact. The problem is that, although there are perfectly serviceable Emacsen written in Common Lisp, none of them are GNU Emacs.

For example, there's Hemlock from CMUCL, and its descendants built into Lispworks and Clozure Common Lisp.

Those implementations aren't likely to work well as a substitute for GNU Emacs. For one thing, there's a substantial ecosystem of software that depends on specific APIs and other characteristics of GNU Emacs. Writing code to bridge GNU Emacs APIs with those available in the Hemlock descendants would be a lot of work.

There are some other obstacles as well. CCL's implementation of Hemlock uses the Cocoa text architecture, so it's not portable to platforms other than macOS.

The Lispworks implementation is portable across Windows and numerous UNIXEN, but the Lispworks license will not allow delivery of a proper substitute for GNU Emacs (it forbids building an application that can be construed as a Lisp development system, and when I pressed them about exactly what limits that policy implies, they explicitly used Emacs as an example of an application that would be forbidden).

The original CMUCL Hemlock and its portable version are designed to work with CLX. It could probably be made to work in a modern X environment, but making it fit well into modern GUI environments and porting it to all the platforms GNU Emacs works on would be a huge amount of work.

I'm probably overlooking some other Emacsen, but I don't know of any off the top of my head for which the situation is any easier.

It hasn't already been done, no. The Emacs variants you mentioned (that IMV should not be referred to as "Emacs") are from-scratch new implementations of just the concept behind Emacs, but not GNU Emacs itself. They are not compatible with GNU Emacs, they don't even support a small fraction of GNU Emacs features, and are thus doomed to obsolescence / non-existent market share.

So far, nobody -that I know of- has tried to move GNU Emacs to Common Lisp. GNU Emacs is a well-known, well-used platform and moving to Common Lisp could very well be worth the upfront costs.

Wishful thinking aside, the GNU Emacs development community has hunkered down behind Emacs Lisp, so improving it will bring immediate and tangible benefits to every GNU Emacs user. I love Common Lisp and do use SBCL for a lot of personal projects, but I also love GNU Emacs and I will take any improvements there that I can get. Watching Emacs Lisp become a more viable general purpose language (improved performance means an expanded set of problems that it can now address) is a great development. Stefan Monnier on emacs-devel:

  The main benefit of such a compiler is not to run existing Elisp
  code faster (99% of existing Elisp code runs fast enough that the
  user won't notice if it runs faster) but to make it practical to
  write other Elisp code which would otherwise be too slow. But for
  that to work well, you want the new compiler to be
  available "everywhere", rather than just on some platforms. So it
  will only start being useful when it works on GNU/Linux, macOS,
  Windows, ARM, RISC-V, x86, amd64, MIPS, younameit (AFAIK
  lbgccjit's CPU coverage is already good enough for that, so the
  main barrier here is the OS support), and when it's not just an
  option at compile-time but when it's included in all builds.

Just when I thought I know enough compsci to understand everything on a sufficiently high level, this guy totally lost me starting from LIMPLE

An important optimization discussed in the video is to optimize through call into C code (i.e elisp->C->elisp). adding RPC at the boundaries would go in the opposite direction.

>You can easily hack the readtable in Lisp

The funny thing about lisp is that all things are easy, but yet, other eco systems offer more finished libraries.