I think it can be a very useful feature in WordPress to add the licence management to the media library. And that would be perfectly inline with WordPress open-source and GNU orientation !
I use CC images on my blog. It is currently quite painful to track the origine, and the kind of licence, including the "machine readable licence" that makes your content available for other searches (Google, Yahoo for example, let you search specific CC content).
Currently, the only option I found was to store that in the description field, and to retrieve it when I want to use an image a second time.
But it would make more sense to have dedicated fields :
- link (different from the link of the image)
- machine readable licence
Of course a plugin could do that, after all it's just adding some meta to the post "attachement", but I think it would make more sense to have it as a core feature. It would put a strong emphasis on this feature, and promote it. I'm quite sure 95% of the users of such content would not look for a plugin, when seeing the fields, they would use it.
I'd be happy to have the feedback of the community on this idea.