By now they (some maintainers and some users) have a lot from a typical Common Lisp into Emacs Lisp re-engineered (incl. the Common Lisp Object System), but it

By now they (some maintainers and some users) have a lot from a typical Common Lisp into Emacs Lisp re-engineered (incl. the Common Lisp Object System), but it is not 'officially allowed' to actually upgrade the language/runtime to it. Just libraries or forks...