I could see it happening by next summer. Business class is full the majority of the time and lots of cargo still in the belly. If an A380 was to come instead of a third daily then that would attract potential EDI customers for Etihad and Qatar if the price was right because people wouldn't mind paying another £20 to go on the A380 apposed to a A330.
A factor for those choosing EDI at the moment could be that those are both morning flight to so people might want to leave earlier and arrive at the destination a bit earlier.