Possible. But not probable. I mean, bungie can't even keep up with cross generation play for the same console family anymore. What hope would they have of letting Xbox and PS play together? Although, as far as I can tell, doing so would be massively beneficial for destiny, since as a p2p game, you need to have a large player base to consistently form lobbies of players with good connections to each other. Furthermore, mixing the Xbox and PS players will also let the Xbox players see first hand how cool the PS exclusives are.