Ticket #27088: show-scheduled-posts.php

<?php
/**
 * Filter `the_posts` to allow viewing of scheduled posts
 * 
 * It can't be done via a capability check because core requires
 * user to be logged in for non-public statuses
 * 
 * @see https://core.trac.wordpress.org/browser/tags/3.8.1/src/wp-includes/query.php#L2972
 */
function dbx_filter_the_posts_show_future( $posts, &$q ) {
        global $wpdb;

        if ( ! $q->is_main_query() || ! $q->is_single || empty( $q->request ) || ! empty( $posts ) ) {
                return $posts;
        }

        $post = $wpdb->get_row( $q->request );
        if ( empty( $post ) ) {
                return $posts;
        }

        $post = get_post( $post->ID );
        if ( 'future' === $post->post_status ) {
                return array( $post );
        } else {
                return $posts;
        }

}
add_filter( 'the_posts', 'dbx_filter_the_posts_show_future', 10, 2 );