This does remind me of the post from the other day about a time traveler. With an expectation that things will get faster, the opposite seems to be the norm. :(
Guile is very low quality software (that goes double, hell, triple, for "non free" platforms like OSX and Windows) and Emacs has a reputation for being rock solid on all platforms it runs on.
The Guile fanboys may wish for Guile to replace the current core in mainline but realistically speaking (Guile has what, 1/2 developers?) that's never going to happen.
If I had to guess, I'd say most Emacs users and developers couldn't care less about Scheme/Guile (if not actively hostile).
I am curious on just how many/what features would be on the table with an alternative vm. And then, how hard it would be to just add those features piecemeal instead of moving whole hog?