Index: src/wp-includes/template.php
===================================================================
--- src/wp-includes/template.php	(revision 34724)
+++ src/wp-includes/template.php	(working copy)
@@ -551,6 +551,16 @@
 		$s = esc_attr( $s );
 	}
 
+	/**
+	 * Filter template file being loaded in load_template
+	 *
+	 * @since 2.9.0
+	 *
+	 * @param string $_template_file Path to template file.
+	 * @param bool   $require_once   Whether to require_once or require. Default true.
+	 */
+	$_template_file = apply_filters( 'template_file', $_template_file, $require_once );
+
 	if ( $require_once ) {
 		require_once( $_template_file );
 	} else {