I still don't see this happening.
So a $399 is about to break even soon, right? (Still selling at a loss in NA, but +/- 0 in Europe, probably same for Japan)
A $100 price cut would mean Sony has to go the way back to a $100 loss per console. After such a huge price cut, the sales will go up, that is for sure. Let's say 10 million consoles will be sold after the price-cut for this year. That would be a $1 billion-loss for this year.
There are rumors, that sony has to report up to a 2.2 billion dollar loss soon. Now try to tell the share holders you are willing to make another billion dollar loss for just ONE division.
And you have to consider that MS will respond in a way. And you just don't want to mess with MS moneywise. Heck, Steve Ballmer alone could buy Square Enix if he wants to :D