https://www.gamespot.com/articles/fortnite-ceo-says-ps4-xbox-one-cross-play-is-inevi/1100-6457675/

Cross-play support between PlayStation 4 and Xbox One is technically possible, but the politics between Sony and Microsoft is keeping it from happening. According to Tim Sweeney, the head of Fortnite developer Epic Games, it is in the industry's best interest to allow gamers on competing platforms to play together, and it's "inevitable" that this will eventually happen. Speaking at the Game Developers Conference recently, Sweeney said PlayStation and Xbox gamers playing together is "the next logical step."

He made his point by referencing Metcalfe's Law. This is the idea that the value of a shared experience is related to the number of people who can connect to it.