I am pretty sure the question is what 'extra' stuff is in Windows Phone 8.1 that only the 1520 gets because of its higher resolution/bigger screen. Extra shortcut in notification centre is all I have seen so far....
Let's hope so!
Also hoping for smaller texts i menues and apps making more information available at the same time. Though it may be a difficult task to make such a universal change show correctly in all existing apps.
Dolby Surround audio recording is supposedly coming to the 1520 and Icon with the Cyan firmware update. The 930 is said to have it at launch. We may get Miracast also. Maybe.