Wii will surely do it. PS3 too, a price cut and a new slim would bump it's sales, plus bigger sales in developing countries. 360 has a harder task, since it is stronger in NA and it's a market that is saturated and will jump more quickly in next gen than the others.
Personally, I believe that there is a lot of gas on current gen. High end PC games aren't that much better than current console graphics to justify a new gen right now. People won't buy new hardware for a marginal upgrade or simply more multimedia capabilities. And this gen started off with a way higher price point. The current prices (after 7 years) are comparable to launch prices in older generations. When the HD twins reach prices lower than $250-150, we'll see a massive improvement on sales. For me, the current low sales aren't because people want a new gen. People want a price cut.
