I get the impression that the majority of emacs users are not averse to learning seemingly weird and dificult new things (otherwise you probably would not have learned to use emacs in the first place). The majority of users are, in my experience anyway, put off by all sorts of things (and often quite unrelated to the merits (or lack of) the language itself). I have also experienced quite a bit of lisp hostility. All of these things add up for me to feel there are better choices as an extension language if you want the average[1] user to write extensions.

[1] by average I mean that they have the technical skill to do so, but aren't terribly invested in learning lots of new things. I imagine (I'm a vim user myself and I find its true for me) that an emacs user has already invested in the tool enough that learning a little more to make it even more useful is not a big deal.

I can't help thinking that your average user is much less likely to write an extension at all. Also, I suspect a disproportionate number of GNU program users sufficiently invested in them to write extensions are either Emacs users already (it is Gnu Emacs, after all) or at least fairly familiar with Lisp.

The sort of person who doesn't go out of his way to learn a new tool is also the sort of person who probably doesn't go out of his way to extend an existing tool either. I think targeting advanced users for writing extensions is completely reasonable.

Plenty of "average" (by your definition) programmers who use Eclipse know Java well enough to write Eclispe plugins. How many of them do? I suspect a large portion of those who do would have written the plugins in Guile as well.

Probably not all that relevant here, but I think that Java's verbosity is a barrier to entry in itself, even if Java programmers do not think so. When I worked in a Java shop a few years ago I would have happily coded up quick extensions and scripts[1] in something like python, but never even considered doing so in Java because there was too much effort involved. I guess I'm arguing that the users must feel that the benefit of writing a script or extension must feel like its much greater than the effort of not doing so and the effort of writing the extension and that Guile is just plain too unfamiliar to most that the effort seems to outweigh the benefits, even if in reality this is not true.

[1] I did actually write a few Python scripts to generate repetitive Java code because I felt that doing so would be much less effort than writing the code by hand.