So the EPiServer.Web.QuickNavigatorMenuItem is used to add items to the QuickNavigatorMenu, its constructor has five arguments, like so:
public QuickNavigatorMenuItem(string caption, string url, string javaScript, string enabledScript, string imageUrl)

But it seems the script rendering you can see if you look at /util/javascript/quicknavigator.js, does this with each item:

 for (key in menuItems) {
                if (menuItems.hasOwnProperty(key)) {
                    alternatives += '
' + menuItems[key].caption + '
';
            }
     }

The javascript, enabledScript and imageurl properties are not even used at all, and indeed you can enter whatever you want in those fields, not affecting the menu rendering.
Also, the ctor summary documentation for QuickNavigatorMenuItem says that url can be left null, but all that will achieve is an menu option that will link to "/null".

Am I missing something obvious here or was this functionality never implmented?