Win the generation? Possible.
Outsell both combined? No chance.
Xbox brand isn't strong enough outside of English speaking countries. Even this generation, with everything going the right way for Xbox, it's struggling to hold 2nd place. It currently isn't the number 1 console in any market and the 1st party content, from what we currently know, isn't strong enough to set it apart from the other 2 in mainland Europe or Japan.
Sony wont make the same mistakes with PS4, as they did with PS3... And Nintendo actually now realise that they need 3rd party support to go along with Mario games.
3rd parties will be giving less exclusives, due to increased costs and a Kinect-like camera for the nextbox wont be as popular as Kinect was.
Next gen will be down to 3 things -
Price
Exclusives
Online Capabilities
Price could go to any, we have no idea yet.
Exclusives, likely to be a Nintendo win. Wii Series, Mario Kart and 2D Mario can/will sell 20 Million units.
Online, again could go any way although probably between Sony/MS. Both consoles excell in different things, will be really interesting to see how services are improved/changed.