Microsoft allows cross platform play

Microsoft is in talks with Sony about cross-play between Xbox One and PS4

With the inevitable widespread adoption of cross play, Microsoft should bring Skype to PS4 so we have a reliable way of cross platform communication : r/xboxone

Xbox One and PlayStation 4 cross-play is not a lost cause, but don't expect it any time soon - MSPoweruser

E3: Xbox extends invitation to cross-platform game-playing

Game on: Xbox One to support cross-platform multiplayer with PS4

Nintendo, Sony And Xbox Start Cross-Platform Functionality

April Fools: Microsoft Strikes Deal with Sony for Cross-Platform Play

Did Microsoft kill Xbox Live+Windows Live cross-platform play because console gamers were too bad?

E3: Xbox extends invitation to cross-platform game-playing