Fred wrote, “I’ve got to say that DC isn’t terribly impressive, given that it’s design seems to magically change for each vaguely possible role it might fill.”

These different roles each have different requirements. It is much easier to modify an existing design for different purposes than it is to restart from scratch. SpaceX chose to modify its existing Dragon cargo ship in order to add human crews, because it is easier than starting over. The Boeing 747 is a good example, as they have made six major variations to cover different customer needs.

Boeing learned in the early days of the jet age that satisfying the customer’s needs is worth modifying a design. Doing so can make a company; not doing so can break a company. Read the article in this posting:
http://behindtheblack.com/behind-the-black/points-of-information/the-707-turns-60/

“They wanted it wider. 4.5 inches wider. They wanted it to be 148.5 inches wide – wider even than the DC-8. This was gut check time. Everything that followed, all of Boeing’s commercial business over the next half-century hung in the balance.”

However, I’ve got to say that DC isn’t terribly impressive, given that it’s design seems to magically change for each vaguely possible role it might fill. If we imagine that these enthusiastic press releases have a basis in reality, then that means that the existing design of DC isn’t actually real, because if it were, then changing to folding wings, or scaling down 50% would not be very easy/cheap/feasible AT ALL.