Too early to say, too many variables.
Core gamers will probably shift towards Sony, but by how much over the long run? People are mad at Microsoft now, but once some time goes by and Microsoft comes out with more and more of its big exclusives, the Xbox brand will recover.
Japan will lean heavily toward Sony, but the home console market in that country is in decline, so running up the numbers there might not make as big of a difference as it did a decade or two ago.
Casual gamers are, I think, the biggest question mark here, though. Nintendo showed with the Wii that they can be successfully wooed if you offer something they want. Nintendo hasn't shown that they are capable of repeating that performance, which means there is a large chunk of potential customers up for grabs (I say potential because it's likely that some, perhaps many, of those Wii owners will only be interested in mobile gaming, though how many, only time will tell). Sony doesn't seem interested in trying to win them over; the price advantage of the PS4 over the will help, but that alone may not be enough.
Microsoft is definitely interested, and their investment in making this happen is the new Kinect. They've made this camera an impressive piece of technology that doesn't suffer from the lag of the original Kinect, and they've fully integrated it into the UI so that multi-tasking is fast and fluid. The question is, will casual games and a motion/voice-controlled UI appeal to casual gamers? I don't know. Maybe. Microsoft thinks it will, and they might not be wrong, considering that the original Kinect has sold over 20 million units. At any rate, if casual gamers start trending toward Microsoft, we probably won't see it until sometime late next year, once X1 early adopters have had a chance to evangelize the console to their friends and family. Until then, I expect Sony will have the advantage.
