Harvey,
Thanks very much for this interesting thread, I look forward to following it.
If I may add one thought to your observations about the limits of what can be usefully made by 3D printing: think hybrid.
Many years ago, I helped introduce the first rapid prototyping machine to one of NASA's largest engineering facilities at Goddard Space Fight Center. We found the possibilities can be greatly expanded by adding strengthening and load bearing materials to the printed structures. Reinforcing rods and plates, as well as bushings and other items can be screwed or epoxied into or onto the printed structure. Think of the printed structure as a framework to position the load bearing components in configurations that would be more difficult to achieve by conventional machining.
Also, at that time, Marshall Space Center was experimenting with rapid prototyping for possible use in space. One of their first prototypes was a Sherline CNC milling machine with a hot glue gun replacing the milling head. Just about any CNC machine could be converted in similar fashion, and fairly quickly restored to conventional milling.
David Clark in Southern Maryland, USA
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