Wu.js (thanks for the link) still looks like Javascript to me and won't cause any problems with Firebug or Emacs. Coffeescript and Objective-J have a completely different syntax. I can believe that Coffeescript is easier to read but it doesn't seem like enough of a win to break tool support and to work in two completely different syntaxes (inevitably there will still be plain js to deal with in most projects).
Objective-J seems even riskier. I can see the appeal for Cocoa people but you're really going all-in with that kind of framework.
