With 3DS, pressing the panic button was necessary. It wasn't selling well. Now that it's selling well, I doubt they're holding out Wii U info just to coddle the 3DS. That would be sabotaging their own plans. As said above, it may be due to short attention span of the masses.
While I don't believe Nintendo or any of the hardware makers would replicate the success they've achieve this gen, it is a bit premature to see how well the Wii U will do. Either way, Wii U would have to fail on apocalyptic level for it to suffer Gamecube's fate.