This is an interesting use case. Implementing something to satisfy it would have clear advantages for users searching Commons.

That said, categories in MediaWiki are a mess. The situation is even worse on bigger wikis like English Wikipedia or Commons. This could cause issues here. For example, Bo (dog) is in a subcategory of a subcategory of Category:African-American people. If one were to search for all images in all subcategories of African-American people, you'd eventually get a picture of a dog. That doesn't seem right. There would have to be a lot of changes to the category structure by users on all wikis to get this to work properly.

Now, structure data for Commons is coming! The structured and reliable nature of the data that will be stored will make something like this much better, e.g. a photo of Bo the dog would tell you it was a dog and not a person. I suspect that building this on top of structured data on Commons, rather than categories, would serve the user need much better.