I believe you can use older classes via "XLite\View\FormModel\Type\OldType" type.
Here is an example from the source code:
PHP Code:
// ...
'images' => [
'label' => static::t('Images'),
'type' => 'XLite\View\FormModel\Type\OldType',
'oldType' => 'XLite\View\FormField\FileUploader\Image',
'fieldOptions' => ['value' => $images, 'multiple' => true],
'position' => 300,
],
// ...
So, you may try something like this with 'oldType' => 'XLite\View\FormField\Textarea\Simple'.
I think this should work.