Is there still any work being done on Guile Emacs? As I recall it basically worked a few years ago, but it doesn't seem to be maintained. I'm curious if these 3.0 speedups would translate there too.
From the Emacs side I strongly doubt it will happen. The discussions that have been going on for faaaar less intrusive changes is staggering. Reading the discussions about the portable dumper (new in the upcoming emacs 27, proposed in 2014) is a nice 4 hours. That was in just about every measurable way a step forward for Emacs, yet it took almost 4 years for it to be mainlined,despite glibc more or less deprecating the old unexec from under emacs' feet.
I might be misrepresenting just about everything here, but one thing I am pretty certain of: guile Emacs will never happen, despite the promises of running elisp on guile.
While this may be the case, my understanding was that once the codebases were combined and guile-emacs builds were brought online, they encountered a severe performance drop from vanilla Emacs due to back-and-forth string conversion between Guile's Unicode strings and the Emacs internal enhanced string type. I thought that the project was abandoned after finding no obvious resolution to the problem short of a complete rewrite of all Emacs string handling.
> guile Emacs will never happen
Universe heat death is still far away, there's always hope.