Emacs Lisp is slow. There has been a multi-decade effort to make Guile support ELisp, and using Guile to make Emacs more performant. Cross platform UI, with a faster Lisp, would allow Emacs to be even more special.
As a non Emacs user, is the speed of Emacs Lisp a frustration in typical day to day usage?
But overall I'm a very happy emacs convert. It's extremely malleable and pleasant development environment and I think it definitely deserves all the gushing articles/posts its been receiving past few years.