They will drop first quarter. PS4 has two big exclusives, one niche exclusive, several smaller exclusives (irrelevant to me, but they are there), and superior performance of multiplats being released right out of the gate.
I still believe that the X1 can match 360 lifetime with the right moves, but PS4 will own the first half of 2015 and will likely secure the second half as well (by a much smaller margin).








