appcommunity-include-replies.php

<?php
/**
* Plugin Name: AppCommunity List Activity Replies
* Description: Unnest replies from comment (activity children)
* Version: 1.0.0
* Author: Matt Thiessen
*/

function appcommunity_get_nested_replies( &$replies, $activity ) {
	if( !empty( $activity->children ) ) {
		foreach( $activity->children as $child_activity ) {

			array_push( $replies, $child_activity );

			if( !empty( $child_activity->children ) ) {
				appcommunity_get_nested_replies( $replies, $child_activity );
			}
		}

		$activity->children = array();
	}
}

function appcommunity_include_replies( $act_item, $retval, $request ) {

	$comments = array();

	foreach($act_item['activities'] as $activity) {
		appcommunity_get_nested_replies( $comments, $activity );
		if( !empty( $comments ) ) {
			$activity->children = $comments;
		}
	}

	
	
}
add_action( 'appcommunity_activity_get_item', 'appcommunity_include_replies', 10, 3 );