It is already in the plugin, with an option to turn it off for chains that do not change data like copy to clipboard, as it takes nearly a second on an 5000 books library (more on larger libraries).
Look for a method called refresh_gui in chain_tools.py. Another way to do it is mentioned by Kovid
here and
here.
Edit: The time my method takes is not in refreshing the gui, but in calculating modified book_ids.