And PS4 will be cheaper too (after keeping launch price for so long), which will eat away X1 sales.
X1 Games for HW movement: 2015 > 2016. It'll sell more in Oct-Dec 2015 than it will in Sept-Dec 2016, that alone already makes the YOY task difficult.
Barring a month where something special might happen (big price cut with no response), i'm pretty sure PS4 will win every NPD in 2016, including the holidays.
PS4 will be up YoY, too but they won't eat XB1 sales away. At least not like you expect.
And the XB1 game lineup for 2016 is even bigger than 2015
Gears4, Crackdown3, Scalebound, Sea of Thiefs, QuantumBreak, HaloWars 2, Forza Horizon 2, Recore + possible unanounced games
vs. Halo5, Forza6, TombRaider, Gears Remaster, Rare Replay, Fable
bold prediction, that will probably not happen ;)