I agree. The language advocacy in the linked article is fine as far as that goes, but 17 years after the Tcl wars, it should be possible to evaluate an extension language strategy by whether it WORKS. Sure, guile is powerful and it COULD be used to build all sorts of powerful extensions, but IS it actually used that way?

I would argue that overall[1], guile has had pretty much no meaningful adoption in GNU projects. Emacs is (of course) still using its own flavor of lisp. gdb, which badly needs a powerful scripting language (and which I think was scheduled to have Tcl support when the wars started), still has no good scripting integration. I cannot think of any other major GNU project using guile.

[1] There are certainly some exceptions. Lilypond uses guile extensively and successfully.