Emacs is a fantastic editor (and I think I can say that I am what you call a power user), but Emacs Lisp is a terrible, terrible language. The more I use it, the more I hate it. And it's not because of the lispiness or parens -- Common Lisp was my Language of Choice for many years.

Having an editor that I could extend in a real programming language (and JS is actually very nice once you grasp stuff like prototype inheritance and learn to avoid the... uhm, bad parts) would be simply awesome. And if it was pretty and integrated with OS X I would be willing to pay hard cash for it.