Kotaku Australia: How You’ll Play Far Cry 4 With Friends Who Don’t Own It.
This is interesting, I remember some PSP games having this function nearly 10 years ago.
This way of sharing seems more about the promotion of the title, than the fun of multi player gaming.
The “sender” will receive ten “Keys to Kyrat” which he can send to ten PSN “friends” of his choice. The “friend” will receive a single unique key allowing him to download a PSN exclusive trial version of the game allowing co-op play in the open world with the “sender” for a limited amount of time. XP, loot, etc that the “friend” earns will then carry over if they buy the game.