Thank you for the feature request - indeed it has been requested number of times. We have it logged, and moreover, put the basics of the API for that. It's called LinkedContent. We will use it for the first time in the Profiles, for example, if you are using an avatar from an image gallery, then try to delete that image, the system will warn you.
I'll see if we can push the implementations for the content items as well, in the near future. We are going to publish Q2 roadmap soon.
We won't be able to release this before Q3. Still, we do not have a certain date for this feature.