There's some kind of paradox here. You say it's mostly a lisp interpreter, but then, also, mostly editor functionality written in lisp. I'm not sure you can have it both ways...
It's lisp man, of course you can have it both ways. Code is really data, your program is actually your environment, your editor is actually a giant lisp program with a built-in lisp interpreter. Or is it a lisp interpreter with a built-in editor? I dunno. I'm off to install this release :)
"We used the same idea here (in the hybrid technique), that most of the editor would be written in Lisp, but certain parts of it that had to run particularly fast would be written at a lower level"
http://www.gnu.org/gnu/rms-lisp.html
That's the beauty of Emacs. Considering that he built it in the early 80s, you have to wonder if the whole thing couldn't be written Lisp today.