If I remember correctly, in one of the SICP video lecture, Hal Abelson says that s-exprs are equivalent to the the syntax tree of the program and, given a graphical interface, we would be manipulating this tree directly. AppInventor for Android is the most similar thing we have today, and not surprisingly it's based on Kawa scheme. It would be a very powerful mode of code editing, if it wasn't centered around click and drag operations (and limited to android). I think that a modal editor ala VIM, paired with a graphical code-block environment and fuzzy text autocompletion, would be a nearly perfect IDE.