[roel_v]

"The bicycle I rode to work today has:"

Well there's your problem. The point isn't to exactly recreate what we have today. The bike as you own it now is like it is because that's the easiest way to manufacture - rather than stamping it out of a block of steel, they take a couple of tubes and weld them together. If it's easier to 3d-print by making the whole thing in plastic, we'll have to engineer materials that allow this and still maintain enough function to be used like today's bike.

Innovation doesn't have to be constrained by today's standards. The Wright brothers didn't have to replicate the flapping wings of a bird, just building something that would fly was ok.