After reading this thread I thought I'd like toengage in some wild speculation too...
I'm not convinced that we really know what 'vertically aligned' screens means. I think in between translation from the Japanese, and then being relayed via a PR person... it could mean anything. It would mean, so most people seem to think, that there will be two landscape oritentated screens one above each other. Or 'vertical alignment' may mean the screens are in portrait mode.
Now... how about I speculate that this is a follow-up to the VB? I've seen single LCD screens that can display basic parallax 3D by projecting different images to each eye, without the need for stereo glasses. Now what if each of these 3" screens, in portrait mode, display different images to each eye, giving an even better 3D effect?
Or maybe taking the landscape screen idea - what if the whole device splits in two? Imagine that each screen has a controller built in along with its own processor memory and battery - so each could be operated by a different person for collabarative or players v's player games. The link betwen the two could be wireless or just a cable that pulls out when the two halves are separated.
Expanding on the splitting apart of the device - let's think Animal Crossing. The lower screen is your character - their stats, inventory, etc etc. The top screen is your village, where you wander around. Now what if you want to visit your friends village? Well you both snap off your top screens from your NDS, swap them, and attach your friends upper screen to your lower screen. If each half of the NDS has memory, processor, battery and screen this would be possible I think.
I think I have a problem just thinking that this there's nothing more to the NDS that having two screen, one for the main game, one for the map screen or something. I mean how is that different to just having a larger screen and using half for the game and half for the map? Any why would the system need multiple processors for this? (or does it just mean seperate video processors for each screen?)