The obvious interface for such a concept would be to have matching parentheses "snap" into a kind of token field around the corresponding text. It would be pretty easy to then build a kind of raised relief map of code built from nested token fields that suggest elevation changes instead of nested parentheses. All in realtime as the user types, of course.
In the history of Lisps is there such an interface? My gut tells me either a) no, or b) yes, there's a maximally unusable version which was abandoned immediately upon recognition that it would suffice as bait to inculcate newcomers into the cult of Lisp parentheses.
Edit: clarification
You could turn the paren bubbles inside-out like )foo )bar(( but that doesn't look as cool to me as flipping the ramps upside-down like /foo /bar\\ and \foo \bar//.
Instead of nested in-and-out bubbles like (foo (bar)), it could have nested up-and-down ramps like \foo \bar// or /foo /bar\\, to represent a "change of level".
That way you could have positive and negative nesting, and turn programs inside-out!
Y-Combinator:
Y-Uncombinator: