Airbus MFF 380 - 350 not going to happen. The A380 has the original Airbus concept cockpit with additional toys. The A350 was a new design cockpit which got away from the older designs.
The cockpit differences, along with the specifications and performance differences make it a bad MFF option.
EK drivers nearly wrote of an A340 with much more similar cockpits and closer operating weights. Not going to happen in my opinion.
J