On his CV, a British freelance animator says he is "Currently Working on a AAA Next-Gen Xbox Release Title .. for 2013." In a post on his firm's Facebook page from last September, the animator states that he is "working with Rare
on a new title," but cannot divulge any details due to confidentiality agreements. However, he does generically hint that the game "will be big." Combining these two items together, it doesn't seem unreasonable to infer that Rare is probably making a launch window game for the next Xbox.
The Verge's Tom Warren reported a few weeks back that Microsoft's slate of "major launch titles" included "a family game set on an island with Pixar movie-style graphics," which doesn't necessarily seem outside of Rare's wheelhouse given their recent casual, family-friendly Kinect focus.