Apologies, I was also working on this in the unauthenticated_response branch, but hadn't yet pushed.
See #416. Maybe you could look into updating this against the branch?
I think we'll have a few things to iron out along the way to getting this in.

I made my changes on the 'unauthenticated_response' branch, do you mean I should update against master? I'm a little new to the differences between forks, and branches, so forgive me if I am misunderstanding. Here is what git branch -a shows on my local repo:

rromano-air:django-rest-framework rromano$ git branch -a
  master
* unauthenticated_response
  remotes/origin/0.4.X
  remotes/origin/HEAD -> origin/master
  remotes/origin/gh-pages
  remotes/origin/master
  remotes/origin/read_only_fields
  remotes/origin/resources-routers
  remotes/origin/unauthenticated_response
  remotes/upstream/0.4.X
  remotes/upstream/gh-pages
  remotes/upstream/master
  remotes/upstream/read_only_fields
  remotes/upstream/resources-routers
  remotes/upstream/unauthenticated_response 

I see your changes now, and merged. Looks like we were doing the same thing at around the same time. I think you already have the equivalent, so nothing really to merge. Closing this pull req, let me know if I can help out. What's next for 403 vs 401?