Index: src/wp-admin/widgets.php
===================================================================
--- src/wp-admin/widgets.php	(revision 41255)
+++ src/wp-admin/widgets.php	(working copy)
@@ -492,6 +492,12 @@
 	$i++;
 }
 
+/**
+ * Fires after the available widgets and sidebars have loaded, just below sidebars.
+ *
+ * @since 4.8.2
+ */
+do_action( 'widgets_admin_page_blow_sidebars' );
 ?>
 </div>
 </div>