Last thing I heard was that Guile-Elisp (and by consequence Guile-Emacs) is working, but very slow. That can be fixed but requires work. Also, Emacs internally uses a different string representation from Guile. This makes the transition between languages tough and some more glue is required.
IMHO Guile-Emacs is "nearly there". I.e. with just a little more work it could have enough momentum and attract developers to be on the trajectory of becoming the default elisp implementation in the long term.
Having the new Guile 2.2 VM drive Emacs would definitely improve things. And the C-codebase could become considerably smaller and cleaner.
Until Guile will work natively on all major operating systems, I see no future for GuileEmacs.
I really can't understand the objections from some people in Emacs land, except for those that would prefer a Common Lisp-based Emacs, but that's not what we've got. We've got Guile, and while that might not be as great as Common Lisp (in their eyes, not mine, for me Scheme is preferable), it's still a lot better than elisp. Rejecting Guile and sticking with elisp just makes no sense to me at all.
Keep in mind that having emacs be based on Guile does not mean that all the elisp emacs packages have to be jettisoned. They will still run as elisp under Guile, and you can continue writing scripts in elisp and have them continue to run under a Guile-based emacs.