Yeah I heard Michael Pacter on one of his GT conference videos saying Sony are gonna market move as a replacement for Wii... however at the current price Move is now, Nintendo don't need to worry... and given how long it's taken for the price of the PS3 to drop, Move will probably be off the casual/family gamers radar for many months yet.
Nintendo have enough titles of their own and from third party to run on a little longer, but yes, I think they could well need to start preparing something for 2012.
And perfectly, they've got the 3DS to concentrate on whilst the Wii starts slowing down.