Index: wp-includes/user.php
===================================================================
--- wp-includes/user.php	(revision 21261)
+++ wp-includes/user.php	(working copy)
@@ -1000,6 +1000,9 @@
 
 	$query_args = wp_array_slice_assoc( $r, array( 'blog_id', 'include', 'exclude', 'orderby', 'order', 'who' ) );
 	$query_args['fields'] = array( 'ID', $show );
+	
+	$query_args = apply_filters( 'dropdown_users_args', $query_args, wp_is_large_network( 'users' ) );
+	
 	$users = get_users( $query_args );
 
 	$output = '';