Your assumption may not be far off. Look at the photo on post #4. It could be used to bring body sections in from China and/or Japan for final Assembly here. That is no secret, Boeing has been talking about the possibility of flying body sections in instead of putting them on a ship like they do now for the 767 from Japan. This shipping body sections in from an outside country is a trend among the larger double isle aircraft built in Everett. Cutting the shipping and lead time is a good thing. But there is a downside – manufacturing jobs in the U.S. are going over seas as we give up work airplane section at a time just as leverage to get big orders and compete with Airbus, (which is doing the same thing).
What worries me more is the next generation of the single isle aircraft. Today the 737 single body section is built in Wichita, shipped by rail to Renton where the wings, engines, landing gear, and interiors are installed. Could the body section of whatever model that replaces the 737 ten or fifteen years down the road fit in a cargo airplane? If so Wichita may have a fight on their hands trying to keep manufacturing from going to China.
IMO, Wichita already has a fight on their hands, in more ways than one.