> Guile-based Emacs is a branch of GNU Emacs that replaces Emacs’s own EmacsLisp engine with the Elisp compiler of Guile.
One Emacs Lisp engine replaced by another.
> Lastly, it will become possible to write Emacs extensions in Scheme instead of Elisp
That means Emacs Lisp remains the implementation language and the extension language. Guile provides the base machine and Guile Scheme becomes another extension language.
Somewhen in the future..
Personally I think that project is misguided anyway, since it would be much smoother to use some Common Lisp as an implementation language (Common Lisp and Emacs Lisp both are based on Maclisp). But Common Lisp is not popular with RMS.
https://www.emacswiki.org/emacs/GuileEmacs
> Guile-based Emacs is a branch of GNU Emacs that replaces Emacs’s own EmacsLisp engine with the Elisp compiler of Guile.
One Emacs Lisp engine replaced by another.
> Lastly, it will become possible to write Emacs extensions in Scheme instead of Elisp
That means Emacs Lisp remains the implementation language and the extension language. Guile provides the base machine and Guile Scheme becomes another extension language.
Somewhen in the future..
Personally I think that project is misguided anyway, since it would be much smoother to use some Common Lisp as an implementation language (Common Lisp and Emacs Lisp both are based on Maclisp). But Common Lisp is not popular with RMS.