In a video which has now been removed from YouTube (via the RPS forums ), a Blizzard rep announced the addition of offline, shared-screen co-op to the PlayStation 4 port of Diablo 3. Whether this is strictly co-op, or will allow single-player offline as well, wasn't specified, but it seems odd that offline play would be present and restricted to co-op. There's no word on whether the feature will make it to PC, and Blizzard tells PC Gamer that it is not yet ready to share anything on the subject.
Offline play has been a highly-requested feature among Diablo 3 players since before release, with its always online model presenting one of the largest controversies in a story that has had more than its share—the infamous "Error 37" connection failure that plagued launch is up there among the most recognizable memes in PC gaming.
Early interviews with Blizzard seemed to suggest that always online was a decision made in order to give us the best version of the game possible. If the PS4 version really has offline co-op, we have to wonder why they're allowed to have "not the best version" and we aren't. The most obvious assumption is piracy concerns.
We'll update you as soon as we know more.