I've heard a lot of people state that Bungie has said yes and some say no to cross platforming. I've seen no news coming out as an official statement from Bungie stating such. If anyone has a link to confirm or deny this I think it would solve this issue. But.....if you paid attention to the Game Informer interviews, specifically Lars Bakken's interview, you would see they only allow communication within your fire team. Secondly, Bakken states that they have functions in place to allow for non-fire team members to communicate. He states the only way to talk across different fire teams is to get into say an xbox party or ps4 party chat. This leads me to believe that cross platforming may happen because they have the tools in place to communicate without speech.