Index: wp-admin/includes/revision.php
===================================================================
--- wp-admin/includes/revision.php	(revision 28632)
+++ wp-admin/includes/revision.php	(working copy)
@@ -211,7 +211,7 @@
 		'fields' => wp_get_revision_ui_diff( $post->ID, $from, $selected_revision_id ),
 	));
 
-	return array(
+	$revisions_settings = array(
 		'postId'           => $post->ID,
 		'nonce'            => wp_create_nonce( 'revisions-ajax-nonce' ),
 		'revisionData'     => array_values( $revisions ),
@@ -222,4 +222,16 @@
 		'compareTwoMode'   => absint( $compare_two_mode ), // Apparently booleans are not allowed
 		'revisionIds'      => array_keys( $revisions ),
 	);
+
+	/**
+	 * Filter the revisions settings used for the revisions JS.
+	 *
+	 * @since 4.0.0
+	 *
+	 * @param array   $revisions_settings The settings array
+	 * @param WP_Post $post               The original post object which owns the revisions
+	 */
+	$revisions_settings = wp_parse_args( apply_filters( 'revisions_settings_for_js', $revisions_settings, $post ), $revisions_settings );
+
+	return $revisions_settings;
 }