It's difficult to say but it does depend on how many Xbox 360 fans stick with Microsoft for the next gen - that'll be an indication of loyalty and how popular it could end up being. There are definitely those who will refuse to buy a Sony console full stop; certain people I know have nothing good to say about the PS3 and, as far as I can see, they won't even consider buying a PS4.
In my opinion the attitude of Sony before the start of this gen with their 'the next gen starts when we say it does' comment seems similar to the powers that be at Microsoft right now with some of the things the're saying.
I just find it refreshing that Sony are producing a games console. Nothing more than it needs to be. We're definitely seeing a different Sony at the moment, fundamentally different from the Sony we knew at the start of this gen.
I might be generalising but the way I see it, Surely almost all PS3 fans (if upgrading) would buy the PS4. I just can't see many at all saying "now is the time to switch to Xbox." With Xbox 360 fans, I can see LOADS of them opting for the PS4 as seen in these threads and in talking to people at work etc. Any newcomers or people that have been out of gaming/skipped a gen, I can't see how they would choose the Xbox. At face value, it's more expensive but beyond that, the deeper you delve, the better the PS4 becomes. Sony have obviously worked hard to ensure they don't mess up another launch and I think they have done a fantastic job. If the better console was £499 and the lesser console was £299 then you could argue all day long about what was the better buy but as it stands, its the first tech purchase I'll make for a while where I'm 100% sure what I want.
Current Amazon pre-orders are 38984 PS4, 2162 Xbox. CBA to do another screen shot.