Think about the developments that occurred recently, and why they may not make so much sense in the current airline climate and improve. This is an idea I just came up with.
First, think about 30 years ago. Regional or feeder lines were mainly prop and short haul. As the new regional jets came about, they replaced those small planes but also allowed faster, longer flights with fewer passengers to fly to airports more frequently than a larger jet and yet still be profitable. You could either fly one 737 per day between Denver and Cincinnati, or several flights of CRJ-700. The downside of these regional jets only came apparent recently with the spike in fuel prices. What is needed now is the carrying capacity of the regional jets (in passenger load and frequency) but with lower fuel costs.
Bombardier came up with their solution, the CSeries, but maybe the smaller 50 seat aircraft is still needed. Maybe take all the new materials and reintroduce the propfan again. You may not get 70% fuel savings but 20-30% or more might be achievable.
If you do not want to design small, then solve the issue the A380s are having with cracks. Heavy jets with minimal numbers of daily takeoffs and landings (the main cause of airframe fatigue) should not have these cracks so soon, so maybe it was a Airbus design error, or just maybe these heavies need a conceptional redesign to minimize airframe stress. Change the way they takeoff and land with a "bounce".
No matter what you think of, think of not only of your design, but why an airline executive would want to purchase your design.