Soundwave on 16 March 2013
Wouldn't surprise me. I doubt the Japanese suits will let them work on some big new unproven IP. The Nintendo that would allow that died a long time ago (go read the Howard Lincoln article).
NCL uses a small handful of Western studios to work on existing Nintendo franchises they don't have time for basically and that's it.
Or it could be that whatever Retro was working on has been put on hold and they've been assigned to help EAD on Mario Kart U, now that Nintendo is in "panic mode" as they've realized NSMBU and Nintendo Land aren't selling Wii Us like they thought and they need Mario Kart for Christmas to save their bacon.
