Thing is, the GBA SP addressed a major problem with then current SP design -- lack of a backlight. The rechargeable battery and sleeker design were definite bonuses, but the backlght was the main advantage. With the proposed Gamecube SP, the main advantage would be DVD playback. For the millions who own PS2, Xboxes, and/or DVD players, DVD playback isn't a feature important enough to make them buy the updated console.
If anything, i'd like it if they released the Q over here, with an updated remote. i'd buy one in a second; i'm a sucker for sexy, yet functional electronics (even though i have a DVD player).