Bungie I hope you know you're player base will jump so high if you add cross-platform. My friend and I fell off the game because of not being able to play together. We are still dedicated to the game but it honestly feels like we are just waiting for D3. I realize it is so much work... BUT PLEASE
My personal idea would almost be like a lobby/server thing. You could choose to play with ps4 or PC or just stay or whatever.