IF I'M PLAYING BF4 ON MY PS4 WHY CAN'T I PLAY WITH FRIENDS PLAYING BF4 ON PS3?
Sony said it would be possible for developers to do this at their own discretion. I can only guess, but, I'm making the assumption that the developers would have to either implement it into two different games, or pay Sony some money for the capability, or both. Hence we probably wont see cross PS gaming in many games. tinstaafl
Everything you need to know about the PS4
Sony has stated that cross-platform play IS POSSIBLE, but the developer has to support it in their games. So it's up to DICE if they want to have PS3 players play with PS4 players. I dont think it will ever happen though.
Warthunder (whenever they finally release it in NA) will be a cross platform game, and you can play it with PC players.
Its all up to the devs.