I believe Sony's plan of first reveal on the 20th of Feb has really put them ahead. They've probably had the system designed and ready to go for some time now.
Couple that with MS's policy changes on DRM and I am almost certain Sony will be out the door first, with far more production.
If this happens, and momentum starts on the PS4, I don't see it swinging back any time soon. All they need to do is show some big games at gamescom and TGS and Sony is going to be on top of the industry with this platform.
GamesCOM is SUPER important for them. EU is their biggest market. If they win over the UK, the only stronghold left for MS is NA, and it doesn't look all that good for them here right now either.
If production is there, and the release date is good, Sony will dominate this gen. It's not like the previous gen where the PS3 offered more power and long term usability over the 360 so that it would catch up late gen. The platforms are extremely similar, there's no reason to be a multi platform owner other than the games. And if you launch at 500$ for 1-2 games, it's not looking good for MS.