|At one point about a year ago I experimented with making indentation significant. I gave up because it was turning into a nasty mess. One thing I learned in the process is that things that in my opinion make Lisp good (the fact that there are no statements, and that anything can go anywhere) make it much harder to represent code unambiguously without parentheses.|
If anyone wants to experiment with it, the code is at http://www.archub.org/noparen.arc .
It's old and may have suffered from bit decay.