According to reports (I read mine at 1up), the GameCube update to the fantastic Mario Tennis series underway at Nintendo's close pals Camelot is making serious progress. In the words of Japan's Nintendo Dream magazine, it's now very much playable.
However Nintendo and Camelot are reportedly keen to put more effort into new gameplay elements in order to create something that even N64 fans will feel is worth picking up on the Cube. A noble ambition if you ask us, and one which seems to have served Nintendo well with Mario Kart: Double Dash, which knocks its N64 predecessor for six.
Mario Tennis is due out in the first half of 2004 according to Nintendo's most recent schedule.