BT Templeton (bipt) has been working (AFAIK in four consecutive GSOCs now) on porting emacs's Elisp engine to GNU Guile. The Guile-folks have been dreaming about this for a while now (see this mail by Andy Wingo from 2010, for example). I'm obviously not an expert, but I was rather sceptical about the chances of success of this endeavour…

Christopher Allan Webber summarises the current state. bipt said on ‘#guile’, that he was successfully performing tasks like reading mail using gnus and using large systems like org-mode on his build of such a Guile-hosted emacs-binary. This is great news indeed. ☺