Lovely rendering, as always, but...
Boeing canned the B757 because the business case was looking shaky. Shame, because it was a great bird.
Correct, at the time. The economies of the 757 started to look unacceptable compared to the 739 and A321.
It was right after 9/11 and Boeing was cutting cost everywhere. Since then global air traffic grew ~4-5% per year.
Looking at how many larger NB's and smaller WB's both Airbus and Boeing forecast, there is significant market demand.
http://www.boeing.com/commercial/cmo...chart2_lrg.gif
Geography shows it too. If you draw a 4000NM circle around JFK, you can see a Billion people, same for Frankfurt; 2 Billion. Singapore: 3 Billion people..
IMO there's no natural gab between 200 seat and 300 seat market requirements. There is just nothing for sale anymore (except, formally, 767s).