It is a long time and I can't say that I will be still playing Destiny in that time, however, it all comes back to what Sony and MS were able to negotiate with Bungie/Activision. Maybe MS thinks that most will jump to Halo when it comes out that they didn't push too hard on Destiny? Maybe Bungie feels the same? Either way Bungie clearly think that what they get from Sony is more than enough to offset any losses on the Xbox side of things. It sucks you have to wait for extra content but the reality is it happens on both sides. PS gets some stuff, Xbox gets other stuff. Up to you to decide where you want to put your money.