I believe someone is working on an emacs in guile. That's the right approach. I don't believe it's necessary or sensible myself. I like Scheme a lot. But Emacs resembles CommonLISP more than Scheme so for Emacs future CommonLISP seems the most sensible option.

Anyway, we're ages away from any of that. Although I do believe we'll see a more capable LISP inside Emacs within a few years now.

I believe there is a google summer of code project to this effect, but as has been said previously in this thread "I'll believe it when I see it".

I think it more likely that Emacs-Lisp will continue to grow on its own incorporating its own threading support and continually reducing the motivations for a rebase overtop of Guile.

Guile already runs emacs lisp itself. There's no need to change the lisp in emacs all in one go to get this to work.