The next Nintendo handheld will probably be a fully online device with a huge amount of internal storage. Knowing Nintendo, their next device will keep the touch screen from the DS but change everything else. The next handheld will only have 1 screen
Also, imagine NO cartridges or disks. I predict that the next Nintendo handheld will have games directly downloaded onto the device through an online store accessible through the device.
Imagine an interface like the Wii Menu except with a touch screen. Imagine having a GPS channel, an internet radio channel, an ONLINE chat and Pictochat channel, a channel which displays what your friends on Nintendo WFC are playing, a channel which has weather, news, traffic, IT WILL BE A LIFESTYLE DEVICE.
Nintendo will try to appeal to all demographics. Also, expect a SHOP channel to download retro GB, GBC, GBA, DS, and other systems games. Lastly, expect an internet browsing channel and a Video Chat channel to communicate with friends.
This device will have the capability to display graphics that are more powerful than the original Xbox on a screen which has a "perfect contrast ratio (true black)"
This device will be amazing.