It would be great if this could be added as a feature. Currently, when you delete a file (say, an image with sensitive or embarrassing content) the thumbnail cache is not cleaned so there's still traces of this file. The only workaround is to manually delete all the thumbnails in ~/.cache/thumbnails (or spend hours hunting down the specific one you want to get rid of). It would be great if the thumbnails would be automatically deleted when you delete the file.
Seems reasonable.