Pure Scheme would not be sufficient. You need at least DOM-handling libraries. And if those libraries were poorly designed, then people wouldn't cotton onto the advantage quickly. Look at DSSSL.
Did you see the '(set! (inner-html (get-element-by-id document "demo")) "Hello JavaScript!")' bit? That's DOM-handling in Scheme. Not a really great API, but it's not terrible either.
Just about every modern Lisp has an X-Expression library, and having used Racket's in production, it's a hell of a lot better than the DOM browsers have today.
