Include and Exclude Taxonomies From Archives & Feeds Using ‘pre_get_posts’

I’ll take another shot.

The following should modify the main query, such that it will include in its loop any posts that belong to no term of the Edition custom taxonomy.

add_filter('pre_get_posts','better_editions_archive');

function better_editions_archive( $query ) {

    if ( $query->is_tax( 'edition' ) && $query->is_main_query() ) {
        $terms = get_terms( 'edition', array( 'fields' => 'ids' ) );
        $query->set( 'post_type', array( 'post' ) );
        $query->set( 'tax_query', array(
            'relation' => 'OR',
            array(
                'taxonomy' => 'edition',
                'field' => 'id',
                'terms' => $terms,
                'operator' => 'NOT IN'
            )
        ) );
    }

    return $query;
}