...from people who seem to refuse to install paredit or coloring plugins for either? ps lisp syntax ftw, it's a feature!
And for anybody thinking of implementing M-expressions, look at Wolfram Mathematica, which is the only popular M-expression-oriented language. It turns out that high-level graph-rewriting semantics are difficult to make efficient! (If you want to try, you might also want to look at GHC or other efficient graph-rewriters to see what the state of the art is like outside Planet Wolfram.)