Rocket League players and developer had made it clear from the beginning that they were hoping to see cross-platform play be a thing in the future. While having the developer on our side might seem like a good thing, nothing can come from them as long as Sony does not give them the green light.
According to the developer of Rocket League, they already have the wrong thing ready and that the only thing that is stopping them from offering their fans the cross-platform play is Sony.
However, they also added that they are not going to give up. According to Jeremy Dunham, they have at least one person in contact with Sony every day in hopes that Sony would finally give in and give them the permission for cross-platform gameplay.
So far, the answers have been no but they are not giving up yet. Sony has never allowed cross-platform play between the PlayStation and Xbox but we are going to keep hoping that the day will come.