Showing the next post’s title, even if it’s an unpublished post

Add these two where you want them to display within your single.php file. It will make the title of the post a link.

<?php previous_post_link(); ?>
<?php next_post_link(); ?>

EDIT:
Sorry I missed the second part of your question about future posts. Here’s what I would probably do. It’s not tested, but will give you an idea.

$adjacent_post = get_adjacent_post(false,'',false) ;
if (get_post_status( $adjacent_post->ID ) == 'publish'){
    echo '<?php next_post_link(); ?>';
}
else {
    echo get_the_title($adjacent_post->ID).' | '. $adjacent_post->post_date;
}