As part of the PlayStation 4's version 2 system update this week, the console will receive Share Play functionality -- a feature that, amongst other things, allows local multiplayer games to be played online.
Share Play utilizes Sony's cloud gaming business to allow PS4 users to share their screen with other PS4 owners. They can then "pass the controller" to a friend online, essentially allowing said friend to play the game as if they were in the room.
Remarkably, this functionality even encompasses multiplayer games that are currently local multiplayer only, such that a PS4 player can share the game online with a friend, and the two can play the local multiplayer game as if they were in the room together.
Both players need to be a PlayStation Plus subscriber to utilize this particular feature, and it can only be used for up to one hour at a time -- at that point you have to quit out of Share Play and reconnect with your friend.
Note that it's limited to two players right now -- and of course, the usefulness of the feature depends on how impactful any latency issues are, as is always the case with cloud gaming functionality such as this.
The update, codenamed Masamune, is due to launch tomorrow - you can read more about Share Play on the PlayStation website