Sources: Boeing, Newairplane.com
quote: that is actually incorrect.if and when a stretch is made is not determined by boeing on its own, but based purely on customer demand. if an airline orders 50 787s, but wants bigger ones, boeing will try to make them. this obviously does take time, but feasibility studies and market studies are done many years in advance.
quote: If Boeing has trouble with one plane they have to halt sales of all new planes