If you're wondering how Nintendo will stay on top by only using the current IP's they have now, well... you're right to doubt them. Depending on old IP's will probably only work if the competition is doing the same.
However, I have confidence Nintendo can create entirely new games for their next consoles to spur the sales. Nintendo has been saying for a while now, customers want new experiences. You can't really do this by recycling older IP's. How would the DS have performed without Brain Age or Nintendogs? The Wii without the Wii Series?
Nintendo knows they need to continue pushing new games to stay on top, so they will do so. They have plenty of time to come up with ideas before this gen finishes.
Btw, Nintendo's IP's are still stronger than Sony / Microsoft's. Those two companies cannot threaten Nintendo without their own new ideas, so it isn't like Nintendo is at some sort of disadvantage (far from it).
