In reply to Sergey Biryukov.

I think it's plugin territory, for now at least.

1. A lot of users use a unique image in each post, so they probably don't need this feature.

2. Without the API changes discussed in the tickets linked from the article, the plugin has to perform several search queries for each attachment displayed on the current Media Library page (or in the media modal). I've made sure the queries are as light as possible, and they work fine in my testing. However, they still might not scale well and can potentially affect performance on large sites with multiple custom image sizes.