The difference between X1 and PS4 multiplat games will be greater during launch than afterwards.
Two simple reasons :
X1 architecture is "esram sauce" complex when PS4 is the first true dev-friendly Sony home console
X1 has an amazing 1st party launch line-up thus offering a lesser return on investment for 3rd parties
Prediction :
2014 : X1 will conquer mainstream channels and audience (thanks to superior UI and kinect)
2015 : 3rd devs will increase X1 budgets putting multiplat games on par or almost to PS4's







