Show missing items in facets exposed filter

Problem/Motivation

We are in the process of switching our site's facets from blocks to Better Exposed Filters, which is a very welcome update. However, we are missing the ability to add a missing result with a customizable label.

Description of the functionality in the block-based format: Show missing - Add a facet item that counts and selects all search results which match the current query but do not belong to any of the facet items. Also has the ability to add "Label of missing items"

Our site is an image database, and in some contexts, browse-ability relies on a missing result. For example, to filter thousands of images to differentiate a general image of a building from an image with more specific details. We also rely on it for internal quality control views, to quite literally find missing items.

Many thanks to all

* Originally posted in BEF ( ✨ Add ability to show missing items in facets Active ), was suggested to post here instead.