This may not be technologically possible, or it may not be cost effective (lack of demand), but I do rather wish that the DS played DS, Advance, AND Gameboy Color/Original cartridges. If the Gameboy Advance could play both Advance and original titles from the same slot, why not have the same functionality in a DS?
A bigger screen would be nice (though will older games be able to take advantage of that?). I like the idea of system interconnectivity, even though I don't currently own a Wii.
I don't really care about music playback or a digital camera feature.