The DS is full of features and stuff we may think that could really make the difference but it facts, it's not going much things. And it's hell no revolution either. What's more, one bigger screen surely not cost the same as two screens. 2 screens games don't need 2 seperate screens anyway.
Sorry, but you have no facts, only your opinion like everyone here. If there is a revolution, it will come from the software, but it´s certain that the games you will see on DS will have a gameplay very different than the ones of PSP, that is the encouraging part.
. 2 screens may not stay.
Just to reinforce my idea, hardware is unimportant, what makes it necesary or important is how the software use it. If the next big thing is a game that use two screen, touch pannel and microphone, well, it would be revolutionary (there is no game that uses all that things)