At LEAST FOUR MORE YEARS. Yeah!!
Nintendo just has begun to show us what is possible on the Wii U.
The Wii U will become the preferred platform for indies when these are "going 3D" as they don't have to compete against AAA 3D graphics. This is happening within the next 2-3 years.
And as we are speaking about Nintendo - they have always the ability to pull of some magic and get the masses of Wii owners to buy a Wii U...