I think he meant Common Lisp macros, a powerful feature of the language (and missing from Smalltalk) that allows one to easily write code that writes code.
Are macros performant enough to allow a power user to replace a scripting language like elisp for a long file of strings, which if I remember correctly was the main issue with using emacs over clisp, unstructured strings.
...but it's a fair thing to think about if the "poweruser" interface encourages creating new macros on the fly. Common Lisp can "compile" at the REPL or otherwise in the live environment.