I have built a plugin that will auto-generate an image based on some variables in the post the user is writing. They have the ability then to set some colors and stuff to make the image look nice. When the user is happy with this image they can click "save". This will call admin ajax and uses wp_insert_attachment to create the image. This much is working.

As part of the ajax call I also call set_post_thumbnail( $postid, $image_id ); to set the featured image. The problem is that this does not update the UI of the post editor. The ajax call returns the attachment ID and image URL. I could manually mess with the dom to insert the image into the featured image box, but I want to know if there is anything in the WP javascript API that will allow me to update the UI of the post editor with this image.