What logic are you using that X1 would win December when it couldn't win Nov? PS4 already sold better on Cyber Monday and remains numebr 1 on Amazon. December follows November in trends and the PS4 is not only the hottest item this fall, but still the most popular gaming console. That won't change for the long run. Those 4 months are long gone and things are back to normal. Xbox has already had it's hype with the release of the Xbox One S and looking to the future people are buying consoles based on up coming games. FF15 is also driving PS4 sales, where as Xbox has nothing to sell it. Gears 4 has performed poorly and Battlefield has dropped after October.
Well PS4 only beat XB1 by 100k, and it was on the same price and in some places had better deals. Also had a Pro model so lots of the sales were from upgrades. With the Pro upgrades slowing down and XB1S deals picking up i think MS will win the month. FFXV isnt an exclusive so for regular casuals its not a deciding factor. Gears 4 is doing less than other Gears but it probably has up to 35% digital so its probably sellinh pretty well. As got BF1 ofc it sales would drop but someone posted here that a gafer said sales were still at 1.3m. If thats true that really good sales.
I already said this before, but it is unreasonable to conclude that FFXV won't be a deciding factor considering that it favors the PS4 by a whole lot. The version that sells more proportionally will inherently have larger word of mouth, which will in turn encourage more consumers to get the console for that particular version than the other. Looking back at March 2010 NPD, the gap between the 360 and PS3 was one of the smallest monthly gap the PS3 had. Granted, God of War III played a significant role at making the gap smaller than usual, but FFXIII sold significantly more on the PS3 than on the 360 by ~435K units despite the latter console having a substantial lead and a FFXIII bundle to reinforce its hardware sales.
Fast forward to now, FFXV looks to sell 80% the PS4 and 20% on the XBO, a far cry from the previous 62.6% PS3 to 37.4% 360 ratio for FFXIII. I don't think the FFXV LE bundle is going to sell all that much, but it could make a difference considering how small November's gap was. And then, we have to consider that Microsoft did not release a new SKU like they did with the blue Gears 4 bundle last month, the PS4 won Cyber Monday, and the PS4's deals go for a longer duration (12/11 - 12/31) than the XBO's (12/11 - 12/24 unless Microsoft also extended the period). Frankly, it's a complete tossup.