Snooping around the internet, I stumbled upon
Gavin Price's LinkedIn profile. He's a Rare designer who has worked on a bunch of the Banjo team games (Ghoulies, Piñata, Nuts & Bolts), Kinect Sports, and some unnamed prototypes. He also has a game scheduled for this year that should be revealed soon.
Further down, it mentions that he's a "Principle Designer" on a project that's been in development for over 2 years, well before Kinect Sports was released; however, since all the previous reports say that Rare's fate rests on the success on Kinect Sports 2, it probably means that they started work on Kinect Sports 2 around the same time as the original (like Back To the Future Part II and III)
I hesitated posting this because his profile used to say that he had an unannounced game for 2009...back in 2010, so this might not be completely accurate. Thoughts?