Growth is going to be enormous for PS4's sales this year, I would say at least 50% increase compared to 2014, market appeal is huge, there are a tonne of exclusives coming, 3rd party sales appeal is going to be in Sony's court even moreso this year for new owners, so sales of over 21M are probably likely this year, just based on the games already announced for the system, with much higher sales than that if the system gets a decent price drop and GT7 releases (which I think is pretty likely), I wouldn't be shocked if Sony has more games to announce for 2015 either.
I think PS4 is set to sell at least 40 million by the end of the year, with 45M+ likely if what I mentioned above happens. In that shipments will definitely be at between 41-46M by the end of this year.
Momentum will carry into 2016, GOW4 could be landing in March 2016, Sony probably has some big exclusive for Feb next year too.
I think PS4 will have shipped 51 million units by March 2016.
