Tag submissions that you've used content from in new submissions.
I think it would be useful if, when making a submission, a user could tag other submissions that they've used content from. For example, if a user is submitting a map and they've used various prefabs, models or MiPs, they could tag those prefab, model or MiP submissions when submitting their map. Those tags would then appear in the sidebar or something, perhaps under the authors, with a link to the prefab.
I believe that people currently tend to either add the prefab author to the authors list or put it somewhere in the description, but a proper tagging system would be nice. It would also be nice if the authors of the tagged submissions were able to be notified when their content is used.