Maybe what Lisp needs to make it popular with kids these days is a hip new syntax.

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:

    \defun Y \f/
      \\lambda \g/ \funcall g g//
      \lambda \g/
        \funcall f \lambda \&rest a/
                     \apply \funcall g g/ a//////

Y-Uncombinator:

    /defun Y /f\
      //lambda /g\ /funcall g g\\
      /lambda /g\
       /funcall f /lambda /&rest a\
                    /apply /funcall g g\ a\\\\\\