fieldable-panels-pane--promo-block.tpl.php

<!-- No PHP in the template, even though it has the PHP extension on the file. -->
<div class={{ classes }} pod">
  <div class="pod--inner">
    <h3>{{ title }}</h3>
    {{ image }}
    <p>{{ promo }}</p>
    {{ link }}
    <p><small>{{ terms }}</small></p>
  </div>
</div>

promo_block.js

/**
 * This is all angular. Consider this a total guess as to the angular code itself, 
 * but the process of grabbing the data from Drupal is straightforward.
 */
var app = angular.module('myapp', [])
.controller('promoBlock', function($scope, $http, $log) {
  $variables = Drupal.settings.promoBlock.variables;
  
  // Now we can grab the values out of the object as necessary and do what we want
  $title = $variables['title'];
  // ...
  
  // We can also call any external services, modify the values, add extra info, etc.
});

promo_block.module

<?php
/**
 * Preprocess function for fieldable-panels-pane.tpl.php
 * We are only using this to grab the information from the promo block widget
 * and pass it to javascript.
 */
function sprint_preprocess_fieldable_panels_pane(&$variables = array()) {
  if ($variables->type == 'promo_block') {
    // This is the bridge between PHP and JS
    drupal_add_js(array("promoBlock" => $variables), 'setting');
  }
}