toffeez, its not a 757 replacement.
It an aircraft covering medium long flights up to 250 seats.
That segment is now covered by the A300, A310, 767-200, 767-300, 757-200, 757-300 and Tu154.
Looking at market forecasts from both Airbus and Boeing for big single aisles and small twin aisles, you see several thousand in demand to replace the existing fleets.
http://theblogbyjavier.files.wordpre...ecast20111.png
The investment would be several Billion, but the ROI / NPV would probably be positive very fast. Airbus is already reaping the benefits of dominating the above 200 seat segment. It would hurt the 787-8, the smallest new WB.
Nothing is as good as being the sole offering in a sizeable niche. The 737-9 Max cannot be stretched any further. Before Boeing had to go with the MAX, they were preparing the NSA, significantly larger then the 737, a 2-3-2 small twin aisle..