Official numbers released by Sony.
A. 1 million sold as of November 16th
http://www.ign.com/articles/2013/11/17/playstation-4-sales-pass-1-million-in-north-america
B. 2.1 million sold as of December 1st
http://www.ign.com/articles/2013/12/03/ps4-sells-over-21-million-units-globally
C. 4.2 million sold as of December 28th
http://www.ign.com/articles/2014/01/07/ces-playstation-4-sales-pass-42-million
D. 5.3 million sold as of February 8th
http://www.ign.com/videos/2014/02/18/ps4-sales-are-currently-at-53-million-units
E. 6 million sold as of March 2nd
http://www.ign.com/articles/2014/03/04/ps4-sales-pass-6-million-following-japanese-launch
F. 7 million sold as of April 6th
http://www.ign.com/articles/2014/04/16/playstation-4-sells-over-7-million-units
PS4 has sold 7 million unites in only 4 months & 23 days or 143 days, that is 48.951 units per day, incredible I know! If PS4 can keep its momentum going through the remaining 269 days of 2014, than we will be looking at 20 million sold.
Personally I think it will reach 20 million. Usually a company ramps up production going into the last quarter of the year. October, November & December could potentially deliver the "final" blow if supply is there.
Major releases/events
May - Watch Dogs (PS4 marketing & bundle)
June - Sony's 2014 E3 Press Conference
August - Madden NFL 15
August - Sony's 2014 GC Press Conference
September - Destiny (PS4 marketing & bundle)
September - Sony's 2014 TGS Press Conference
September - FIFA 15
October - Dragon Age: Inquisition
October - Batman: Arkham Knight (PS4 marketing & bundle)
October - Battlefield
November - Assassin's Creed: Unity (PS4 marketing & bundle)
November - Call of Duty
And then we got games like;
The Order: 1886
DriveClub
The Last of Us: Remastered
MLB 14: The Show
EA Sports UFC
NBA 2K15
Evolve
Dying Light
The Crew
Lords of the Fallen
And many more.