@Artha - there is currently no way for plugins to be launched from the edit metadata window. I agree it could be extremely useful if it were possible. My main usage would actually be the extract ISBN plugin, though you would get into a mess with not being able to click on the extract complete dialog until you closed the Edit Metadata dialog without implementing some differing logic.
I can't even find a way to view a book format from that window - is there a way I am missing? You can add/delete, extract from them but not view them?