From MagicBox:

- David Gosen of Nintendo confirmed that the company is already developing a successor of GameBoy Advance, and it is a different system from Nintendo DS. The launch time of the system will base on how well the Nintendo DS will do in the market. If Sony PSP gains more market share, Nintendo will launch the successor of GameBoy Advance as early as 2006, otherwise the launch time will push back for another year (which is 2007).

It' s not the fact that they' re developing a GameBoy Advance successor, it' s that they' re planning to release it so soon after the DS if the PSP becomes a hit.

They may claim that the DS is in a different category than the GameBoy Advance and its real successor but in some peoples' minds I think the only thing that will register is that Nintendo has released two handheld units within a very short time frame of each other, which some may see as some type of warning sign.

I' d rather see them pull the DS from production, return to the drawing board and combine the idea of the DS with the specs of their GBA successor and release only that unit in 2006.