Three years ago, I wrote about a talk by Andy Wingo on the new Guile architecture. One of the most interesting things in the talk for me was Wingo's plans to integrate Guile into Emacs by replacing the Elisp engine with the Guile engine. Guile already has an Elisp mode so the idea is that existing packages wouldn't need to be rewritten and new code could be written in either Elisp or Scheme.
Since that talk I haven't heard much about the project except for an occasional question on reddit or HN as to whether it was still alive. It turns out that it is alive and one of this year's Google Summer of Code projects is to complete the integration of Guile into Emacs.
Sadly, I can't find much useful information about the project but this article on the Emacs Wiki gives some useful background. It's not clear that the Emacs maintainers would accept Guile as the new Emacs engine so Guile-Emacs may be just a curiosity. On the other hand, it may turn out to offer enough advantages that it does get accepted. It will be interesting to see what happens.