Turkish on 07 January 2017
I'd say the entire library, past and upcoming is the system seller.
The obvious big games like Destiny 2, RDR2, GTA6, FF7R, GT Sports etc are coming.
But someone else is interested in the system because of the amazing back catalogue.
Another may be interested because PS4 gets all the niche games he/she wants.
So accumulating all this makes a huge install base for PS4.
