Custom menu walker to generate integrated breadcrumb dropdowns

Have been trying to write a custom walker class which returns a wp_custom_menu as follows.

http://i.stack.imgur.com/lC5cP.png

Planning to enhance the different states with some scripting. The page at http://www.htmldrive.net/items/demo/169/jQuery-Plugin-xBreadcrumbs-Extended-Breadcrumbs-navigation is a good example of the planned end result.

Could not find any leads nor howtos, some ideas would be fabulous!

Many thanks,

F.