Workaround for embedding non-image media in WYSIWYG

gistfile1.aw

<?php

/**
 * Implements hook_media_token_to_markup_alter().
 *
 * Allow non-image files to be embedded in the WYSIWYG by converting the
 * 'preview' markup to be shown in the WYSIWYG to an image preview of the file.
 */
function custom_media_token_to_markup_alter(&$element, $tag_info, $settings) {
  if (!empty($settings['wysiwyg']) && $tag_info['file']->type != 'image') {
    $element = media_get_file_without_label($tag_info['file'], 'media_preview', $settings);
  }
}

/**
 * Implements hook_form_FORM_ID_alter().
 *
 * Alter the media embed form to show to the user that the file will only be
 * shown in the WYSIWYG as a preview and not the actual file contents.
 */
function custom_form_media_format_form_alter(&$form) {
  if (!empty($form['#media']->override['wysiwyg'])) {
    foreach ($form['#formats'] as $view_mode => $preview) {
      $element = media_get_file_without_label($form['#media'], 'media_preview');
      $form['#formats'][$view_mode] = drupal_render($element);
    }
    $form['heading']['#suffix'] .= '<div class="messages warning">' . t('This media will be shown as a preview in the WYSIWYG since it is not an image.') . '</div>';
  }
}