Can you tell us how you plan to develop the game? I don't know how you'd be able to show your game to Nintendo, but even if you could, I doubt they'd like you doing it without their sdk. I asked how you plan to develop the game, because if it's in something like c++, it's easy to separate the graphics engine from the the core systems. This would allow you to make a pc demo, and quickly port it to the DS.
Although, it's probably worth considering the hardware of the DS while developing the game, there is a hardware accelerated tile system that you'd probably use.