Custom bbpressRecent replies shortcode.

bbpress_recent_replies-shortcode.php

<?php

/*
 * Get the most recently replied-to topics, and their most recent reply
 */
function custom_bbpress_recent_replies_by_topic($atts){
  $short_array = shortcode_atts(array('show' => 5, 'forum' => false, 'include_empty_topics' => false), $atts);
  extract($short_array);
  
  // default values
  $post_types = array('reply');
  $meta_key = '_bbp_last_reply_id';
  
  // allow for topics with no replies
  if ($include_empty_topics) {
    $meta_key = '_bbp_last_active_id';
    $post_types[] = 'topic';
  }
  
  // get the 5 topics with the most recent replie
  $args = array(
    'posts_per_page' => $show,
    'post_type' => array('topic'),
    'post_status' => array('publish'),
    'orderby' => 'meta_value_num',
    'order' => 'DESC',
    'meta_key' => $meta_key,
  );

  // allow for specific forum limit
  if ($forum){
    $args['post_parent'] = $forum;
  }
  
  $query = new WP_Query($args);
  $reply_ids = array();  
  
  // get the reply post->IDs for these most-recently-replied-to-topics
  while($query->have_posts()){
    $query->the_post();
    if ($reply_post_id = get_post_meta(get_the_ID(), $meta_key, true)){
      $reply_ids[] = $reply_post_id;
    }
  }
  wp_reset_query();
  
  // get the actual replies themselves
  $args = array(
    'posts_per_page' => $show,
    'post_type' => $post_types,
    'post__in' => $reply_ids,
    'orderby' => 'date',
    'order' => 'DESC'
  );
  
  $query = new WP_Query($args);
  ob_start();
    // loop through results and output our rows
    while($query->have_posts()){
      $query->the_post();
      
      // custom function for a single reply row
      custom_bbpress_recent_reply_row_template( $query->current_post + 1 );
    }
    wp_reset_query();
  
  $output = ob_get_clean();
  return $output;
}
add_shortcode('bbpress_recent_replies_by_topic', 'custom_bbpress_recent_replies_by_topic');

/*
 * Executed during our custom loop
 *  - this should be the only thing you need to edit
 */
function custom_bbpress_recent_reply_row_template( $row_number ){
  // get the reply title
  $title = get_the_title();
  
  // optional title adjustments -- delete or comment out to remove
  // remove "Reply To: " from beginning of title
  $title = str_replace('Reply To: ', '', $title);
  
  // trim title to specific number of characters (55 characters)
  $title = substr( $title, 0, 55);
  
  // trim title to specific number of words (5 words)...
  $title = wp_trim_words( $title, 5, '...');
  
  // determine if odd of even row
  $row_class = ($row_number % 2) ? 'odd' : 'even';  
  ?>
    <div class="bbpress-recent-reply-row <?php print $row_class; ?>">
      <div><?php print $title; ?></div>
      <div>Excerpt: <?php the_excerpt(); ?></div>
      <div>Author: <?php the_author(); ?></div>
      <div>Link To Reply: <a href="<?php the_permalink(); ?>">view reply</a></div>
      <div>Link To Topic#Reply: <a href="<?php print get_permalink( get_post_meta( get_the_ID(), '_bbp_topic_id', true) ); ?>#post-<?php the_ID(); ?>">view reply</a></div>
      <div>Link To Topic/page/#/#Reply: <a href="<?php bbp_reply_url( get_the_ID() ); ?>">view reply paged</a></div>
      <div>Date: <?php the_date(); ?></div>
      <div>Avatar: <?php print get_avatar( get_the_author_meta( 'ID' ) ); ?></div>
      <div>Time Ago: <?php print human_time_diff( get_the_time('U'), current_time('timestamp') ) . ' ago'; ?></div>
      <div>bbPress Profile Link: <?php print bbp_user_profile_link( get_the_author_meta( 'ID' ) ); ?></div>
      <div>Avatar linked to bbPress Profile:<a href="<?php print esc_url( bbp_get_user_profile_url( get_the_author_meta( 'ID' ) ) ); ?>"><?php print get_avatar( get_the_author_meta( 'ID' ) ); ?></a></div>
    </div>
  <?php
  
  // Refs
  // http://codex.wordpress.org/Template_Tags#Post_tags
  // http://codex.wordpress.org/Function_Reference/get_avatar
  // http://codex.wordpress.org/Function_Reference/human_time_diff
  // (template tags for bbpress)
  // https://bbpress.trac.wordpress.org/browser/trunk/src/includes/users/template.php  
  // https://bbpress.trac.wordpress.org/browser/trunk/src/includes/replies/template.php
}

// allow shortcodes to run in widgets
add_filter( 'widget_text', 'do_shortcode');
// don't auto-wrap shortcode that appears on a line of it's own
add_filter( 'widget_text', 'shortcode_unautop');

Optimized queries version: https://gist.github.com/daggerhart/4244c147f47a6bd95255

Updated to allow for recent topics that don't yet have replies.