An industry source has told Kotaku that:
After the next generation of machines comes out, Wii U will be a performance orphan. It will be closer in performance to the next iPad than the next-gen machines.
That in itself doesn’t spell doom for Nintendo, of course, and it’s impossible know when these sources have any biases that might affect their judgement of what should be a purely fact-based argument. To dive deeper into a perspective on where the Wii U is heading, you might want to read the full report.