I was clarifying terminology for you, as you seemed confused as to what a widget is. That out of the way:

• It's already possible to place a shortcut to the File Manager on the desktop.
• Shortcuts simply open applications. They don't offer any configuration options that allow a user to specify a particular action (such as going to a given directory) an application should take when it launches.
• Depending upon what command line arguments and D-Bus signals the File Manager accepts, if any, it may be a simple matter for a developer to create a widget that tells the File Manager to launch and display a particular folder.