It would have to be free, otherwise they become customers. The current option is to pay for an apple device.
Ok, should Sony be _required_ to support playing playstation games on an Xbox if people are willing to pay?
Communication protocols and interactive 3D software applications are not at all equivalent.
Going down the protocol route here - this would be more like Sony blocking game developers from allowing interoperability between Playstations and Xboxes. Crossplay is most definitely a thing - without requiring Xbox versions of games running on Sony hardware.