Going off of VGChartz numbers PS4 has sold 11,447,553 up until the week ending 4/10/2014 numbers.
By 4/1/2014 it had sold 4,425,130.
From 4/1/2014 to 4/10/2014 PS4 sold 7,022,423, if holiday sales account for 50% of the year's totals than around another 7 million from October to the end of December, PS4's total should be around 18.5 million by the end of the year.
If PS4 has in fact sold around 12 million by the 4th of october (which I think is likely) then the year's totals would be 7.6 million, that would make the total by the end of this year 19.6 million.
I suppose most would consider that way too high, probably thinking Sony couldn't produce that many, but I doubt Sony stayed at producing only a million a month, they'd like gradually ramp it up over the course of the year, because they wouldn't want to run out like they did at the launch.
An average of about 1.26 million a month for the year, plus whatever they shipped between the period before launch, right up to the start of Jan would probably give them about 20 million units to ship, so more than enough to meet demand for the time PS4 has been on the market.
17 million by the end of the year is easy and probably well below what the console will actually sell through by the end of this year.
Personally I'd expect at least 18.5 million, I'm not sure how reliable the whole thing of selling 50% of all sales in the holiday period is, but if it is reliable then people should expect 19.6 million units to have been sold by the end of this year.
