As measured by what? Clojure is pretty popular, as is Racket in other circles. Common Lisp is robust, standardized, and "decentralized" with both free and commercial implementations. It and Python power a few quantum computing technologies.
https://emacsninja.com/posts/state-of-emacs-lisp-on-guile.ht...
I mean, I'm sure I could write a fast enough GB emulator with Guile.
Not with Elisp, even with the XCB or XLIB bindings for Elisp/Emacs.
Which makes me wonder – instead of trying to port GNU Emacs to run on top of Scheme, might it be easier to produce a Scheme implementation that ran on top of Emacs Lisp? Possibly Emacs Lisp is missing some of the primitives required to implement Scheme efficiently, but the amount of code required to add those primitives will likely turn out to be less than that required to reimplement the whole of GNU Emacs in Scheme – and adding those new primitives may make Emacs Lisp a better language, thus benefitting even those users who aren't interested in Scheme in itself.