I have been thinking about it for some time and here it is. Although it is not very usable with most of the default Drupal themes, it certainly could. Currently it looks OK only in Bluemarine and Pushbutton themes. However, it doesn't clear the floats (?) and this is why other element over lapses the menu and the superfish-navbar menu type looks seriously corrupted.
The script as well as some examples of its usage are available at http://users.tpg.com.au/j_birch/plugins/superfish/.
My patch adds 3 new menu types (superfish-horizontal, superfish-vertical and superfish-navbar), moves conditional JS and CSS loading theme_nice_menu() as it seems that caching is disabled for the module and adds some information to the block configuration form as well as to the README.TXT file.
Apply it with
patch -p0 < nice_menu_superfish.patch.
Progressive (that is without JS it still looks and behaves as a Nice Menu) enhancements provided by the Superfish script:
- dynamic width of the menu items
- animation of the dropdown
- shadows in all browsers except IE 6
- hoverIntent plugin allows a delay of mouseover and mouseout events to avoid accidental vanishing and appearance of the menus
It certainly needs some further work. TODO:
- make some kind of CSS reset for nice_menus to allow it to work in all themes
- detection if the Superfish script is available
- better customization
- better documentation