If you look at almost any modern airliner's development cycle, you will see that a significant period of time was spent simply developing the specifications in

If you look at almost any modern airliner's development cycle, you will see that a significant period of time was spent simply developing the specifications in collaboration with the airlines. I am not familiar with any commercial jet that has been developed without commitments from airlines to buy it. Even the DC-3 was developed in response to a request from TWA for something similar to the Boeing 247.