Actual Numbers for X1, PS4 and Wii U after Week Ending 13th Dec

[Kerotan]

Nate4Drake said:
PS4 : 16.4M by week-ending Nov 29th, undertracked by VGC by 300k.
17.1M by week-ending Dec the 6th.
18.0M by week-ending Dec the 13th.
19.2M by week-ending Dec the 20th.
20.5M by week-ending Dec the 27th.
20.8M by the end of the Year.

Good guess. I'll go with something similar but my final number between 20M and your number.