Some features that are missing right now:
1. A proper list structure instead of arrays.
2. Macros
3. A richer numeric tower.
4. FFI
What other major changes are needed in ecmascript before the bastard child of cl comes of age, to become the new lisp? Or is there something big I am missing which makes it impossible?
John Resig has a nice overview of Ecmascript 5 at http://ejohn.org/blog/ecmascript-5-strict-mode-json-and-more/
Plus tail call optimization is coming soon to SpiderMonkey, https://bugzilla.mozilla.org/show_bug.cgi?id=445363