This new plane, if built, will not fly in the same flight patterns as the average commercial passenger or military aircraft. This type of aircraft typically flys at high altitudes, on the edge of space where the atmosphere is thin. Therefore, no need to worry about trivial concerns like birds ingesting and excess fuel consumption. With little air resistance, fuel consumption is minimal. Most likely, less than that of the Airbus A 380. Odd, no one is complaining about the amount of fuel that huge plane consumes.

As far as the discomfort of flying on the SST... Have you tried Northwest Airlines? The seats push against your knees and hold you there until you disembark, if you're able to when you arrive. After one cross-country flight with that Co; Never again!