Chinese website WeiPhone posted photos of what is allegedly the back casing for the iPad mini 2, or whatever Apple decides to call it.
It looks a lot like the current one, as Electronista reports, but seems thicker. However, they say that it could be because the one in the photo doesn’t have the angled edges that the current mini (and iPhone 5) have.
It’s also reported that the slightly thicker look my indicate a Retina display. The full-sized iPad grew a bit thicker when it got a Retina display.