Unfortunately I don't think DKC is going to perform all that great. Maybe 2.5 million LTD over a long period of time.
The system is over-saturated with platformers (again poor planning on Nintendo's part), heck the system comes with 1 1/2 platformers bundled right from the get go.
I think sales will indeed sag quite a bit from Jan-March. Mario Kart is where they basically have to make their big stand I think. Price cut for sure around there if not the nuclear option of a gamepad-free SKU for an even deeper possible price drop.