PD started the GT6 development years before the first PS4 devkit be out.
Now I will make a question for you guys...
Did you wait until late 2014 or 2015 to GT6 be released on PS4 or late 2013 for PS3?
Said that... PD already started the development of GT PS4 since last year but the game will be ready only in late 2014 or 2015.
Anybody that expect PD do create a GT from nowhere for PS4 launch is crazy... you need time to make a game like Gran Turismo because you can do the game like you want... you need to use real life data to make everything in this game... this opition (GT6 on PS4 at launch) never existed.
PS. To make a comparison... the other racing franchise is loosing features to be released at launch... PD never will do that... each game is a incremental... features are polished and new ones added.