Agregar campos personalizados a la configuración de la galería nativa wp

Gracias por tu código. He investigado este problema más a fondo (esto no es un problema de formato de enteros). La única solución que se me ocurrió para los campos numéricos es parchar el mono más WP JS. Aquí hay un código completo con modificaciones que admite cualquier tipo de entrada:

add_action('print_media_templates', function(){
?>
<script type="text/html" id="tmpl-custom-gallery-setting">
    <h3>Custom Settings</h3>

    <label class="setting">
        <span><?php _e('Text'); ?></span>
        <input type="text" value="" data-setting="ds_text" style="float:left;">
    </label>

    <label class="setting">
        <span><?php _e('Textarea'); ?></span>
        <textarea value="" data-setting="ds_textarea" style="float:left;"></textarea>
    </label>

    <label class="setting">
        <span><?php _e('Number'); ?></span>
        <input type="number" value="" data-setting="ds_number" style="float:left;" min="1" max="9">
    </label>

    <label class="setting">
      <span><?php _e('Select'); ?></span>
      <select data-setting="ds_select">
        <option value="option1"> 'Option-1' </option>
        <option value="option2"> 'Option-2' </option>
      </select>
    </label>

    <label class="setting">
        <span><?php _e('Bool'); ?></span>
        <input type="checkbox" data-setting="ds_bool">
    </label>

</script>

<script>

    jQuery(document).ready(function()
    {
        _.extend(wp.media.gallery.defaults, {
        ds_text: 'no text',
        ds_textarea: 'no more text',
        ds_number: "3",
        ds_select: 'option1',
        ds_bool: false,
        ds_text1: 'dummdideldei'
        });

        wp.media.view.Settings.Gallery = wp.media.view.Settings.Gallery.extend({
        template: function(view){
          return wp.media.template('gallery-settings')(view)
               + wp.media.template('custom-gallery-setting')(view);
        },
        // this is function copies from WP core /wp-includes/js/media-views.js?ver=4.6.1
        update: function( key ) {
          var value = this.model.get( key ),
            $setting = this.$('[data-setting="' + key + '"]'),
            $buttons, $value;

          // Bail if we didn't find a matching setting.
          if ( ! $setting.length ) {
            return;
          }

          // Attempt to determine how the setting is rendered and update
          // the selected value.

          // Handle dropdowns.
          if ( $setting.is('select') ) {
            $value = $setting.find('[value="' + value + '"]');

            if ( $value.length ) {
              $setting.find('option').prop( 'selected', false );
              $value.prop( 'selected', true );
            } else {
              // If we can't find the desired value, record what *is* selected.
              this.model.set( key, $setting.find(':selected').val() );
            }

          // Handle button groups.
          } else if ( $setting.hasClass('button-group') ) {
            $buttons = $setting.find('button').removeClass('active');
            $buttons.filter( '[value="' + value + '"]' ).addClass('active');

          // Handle text inputs and textareas.
          } else if ( $setting.is('input[type="text"], textarea') ) {
            if ( ! $setting.is(':focus') ) {
              $setting.val( value );
            }
          // Handle checkboxes.
          } else if ( $setting.is('input[type="checkbox"]') ) {
            $setting.prop( 'checked', !! value && 'false' !== value );
          }
          // HERE the only modification I made
          else {
            $setting.val( value ); // treat any other input type same as text inputs
          }
          // end of that modification
        },
        });
    });

</script>
<?php