Besides, do you think Sony will ever allow PC/PS4 gamers to play together?
Yes, absolutely. Because having that happen has already been committed to. PC and PS3 players play together in Final Fantasy XIV (just like PC and PS2 (and XBox 360) players play together in Final Fantasy XI). When the PS4 edition of Final Fantasy XIV comes out (it's already in beta), they will play together with the PC and PS3 players.