Xbox One, Just like PS3 will come back and sell very high, They already signaled they will drop price, meaning will well see a price cut in the Fall. Most likely $100 off. This will push numbers very high for XBox One. The launch was very successful and looks like they just need the price to be right. The ones not buying in, obviously think $500 is just to much and to many it is. However $399 would be acceptable I think. So No I don't Think PS4 will get 50% market Share. It's only a matter of time before MS makes some major moves and this will stimulate sales.
Microsoft has never signaled a price drop, the only thing they did is 30 bucks in the UK... Microsoft probably wont do a $100 price drop until they can manufacture the Xbox One for $100 less, or unles they drop the Kinect out of the package (which they wont). Because if they would, you'd start selling the Xbox One at a loss, which is the last thing you want to do.