As the supply chain becomes more mature, as the production facilities in Europe and in Fort Worth, Texas, become faster and more efficient, and with the scales of quantity—as you start getting up to the point where you're delivering an aircraft every 1.5 days with a moving production line--clearly it will be more efficient, and those estimates of unit price will continue to come down to some point where they will bottom out.
On June 14th, 2011. See this statement in context.