It's not the fault of the developers as to why there isn't split screen anymore, it's the hardware the games are working on. Looking at Battle Field and Killzone, for example, both have extreme resolution, sometimes resulting in lag. This is a testament to the weight load these games have on the hardware, with Destiny just as big, and will only get bigger. So, in the end, I do not think split screen will be feasible. But it will be extremely satisfying and surprising if Bungie can pull off this feature along with how big Destiny is.