I would guess that such a change would be too big to be economically viable. Sass would require a rewrite of all the parsing code, and a redesign of the GUI CSS

I would guess that such a change would be too big to be economically viable. Sass would require a rewrite of all the parsing code, and a redesign of the GUI CSS editor. Unless Sass gains a considerable market share among Mac users, I doubt it'll happen. You're better off trying to convince them to include the necessary hooks in Espresso, if they add CSSEdit-style functionality to it.