GDC isn't really the place to expect announcements.. That said, Nintendo has announced various things during their keynote speech in the past such as Virtual Console details, the Wii System update allowing for SD card saving and they have also shown various Zelda trailers.
I could certainly see them showing the Wii Vitality Sensor as a look into the future of the industry (i.e. interface innovation) and a Zelda trailer is certainly possible based on most of their other GDC keynotes.







