Here's why it won't happen with Destiny: (Gaming)

by Blackt1g3r , Login is from an untrusted domain in MN, Monday, March 14, 2016, 16:45 (2976 days ago) @ CyberKN

I would think as long as the games are using the same networking code (and assets of course) it wouldn't really matter what system the game is running on. The harder part for Destiny is the exclusives. Either they need to make you able to transfer your character with the exclusives intact (which might be against the contract for the exclusives), or they need to have some way of requiring your character to remove their exclusives before they can go onto the other platform.