Jesus Diaz of Gizmodo has put together a rather lengthy wish list for the next Nintendo DS, trying to stay as realistic as possible. In compiling this list, Diaz considered what is possible, what has been rumored, and what would actually improve a gamer's DS experience.
For starters, he's hoping for all sorts of "power-ups", including a faster processor and better graphics. This should be fairly easy thanks to all the developments in the cell phone world. Memory expansion via an SD card slot is also a possibility, seeing how Nintendo took that route with the Wii. Other things that are mentioned include an accelerometer, a built-in light sensor, a MacBook-style stealth hinge, a 3.5-inch widescreen on top, a larger touchscreen below, movie playback capabilities, and a two-toned color scheme.