The word “may” is doing a lot of work in that sentence. :)
It seems there’s some worry about the language, but the big issue is the implementation. Transpiling from elisp to Common Lisp doesn’t seem unpossible, which would allow them to use clisp (or maybe sbcl). Then simply keep the user facing language as elisp.
Here’s an old example of loading elisp into Common Lisp: https://github.com/blindglobe/clocc/blob/master/src/cllib/elisp.lisp
I don’t know enough about Common Lisp, Elisp, or Scheme, why would it be harder to reconcile Elisp and Scheme than Elisp and Common Lisp?
Elisp and common lisp are closer in the ancestry than scheme. Common lisp and Elisp are both lisp-2s, for instance.
The main point here though, I think, is that adopting guile has the potential to fragment emacs extensions in a potentially bad way. I’m not convinced that that is true, as I ultimately see as many advantages as disadvantages, but ….