So, consoles usually sell around 50% of their annual total on the holidays. So I did some very simple math to see what can we expect:
PS4
4M by Dec 31, 2013
12M by Sep 31, 2014
8M Jan -> Sep 2014
8M Sep -> Dec 2014
16M - 2014 (Total)
20M - Total by Dec 31, 2014
XONE
3M by Dec 31, 2013
6M by Sep 31, 2014
3M Jan -> Sep 2014
3M Sep -> Dec 2014
6M - 2014 (Total)
9M - Total by Dec 31, 2014
Now my actual predictions are around 18M for the PS4 and 10M for the XONE by 31 Dec 2014. Why? Because XONE sales rely more heavily on the NA market where holiday sales grow the most.