I really doubt the GCN has two years left.
After Zelda Reborn comes out, its pretty much curtains.
There's only room for one "budget" console, and I think PS2 is going to be it by virtue of its wide selection of budget software, market leading brand, sleek redesign, and the impending $99 price drop.
Neither GameCube or XBox will get much support, from developers or retail past early 2006 IMO.