What I wonder is this: the mighty 707 and the KC135 programme were spawned out of the same programme (or at the very least, both programmes were able to draw on the same technology), presumably reducing the per-unit and development costs of both.
The 767, whilst a great aircraft, is over 30-year-old technology (some bit probably older still). If the new tankers mimic the KC135, they'll be around for at least 40 - so that will mean a 70-plus-year-old programme.
It's smart of Boeing to offer a product whose development costs have been fully amortised such that each unit off the line is now basically pure profit (actual production overheads and materials aside).
But if I were the USAF, I would want a new aircraft to operate with my other new aircraft (F22, F35, etc.) - so why is the Pentagon planning on making the "war fighter" of the future, put up with 70-year-old technology? Why are we not seeing a 'KC787'?
The USAF would, at a stroke, be the programme's largest customer by far and would therefore be able to wring keen pricing out of Boeing. If Boeing was smart, it would price competitively on the basis that the KC135 is not the only 707-family variant in USAF service and most of the others will probably need replacing during the life of the new tanker: E3, JSTARS, etc. So offer keen pricing on the new toy now and you have a shoe-in for the follow-ons.
Once the KC767 is done, I reckon Boeing will close the 767 line as they won't want it competing with the 787. Boeing may get a look-in for other programmes using the 787 platform but they won't have the same leg-up as if they'd offered a 787 tanker for this requirement.
Highland Cow,
Boeing's Everett plant has a dedicated ship dock nearby, which is connected to the factory by (what I believe is) the steepest-grade railway in the US. Parts for all Boeing wide-bodies come in from all over the world - Japan, Korea, various European countries, Australia... They are most certainly not "all-American".