I am really thinking that Shanghai will not be revisited this season since Season6. Film crew at Nanjing Road sounds very weird. Nanjing Road is a busy shopping area in Shanghai they could just be using decoys there and sent the real final 4 to a different location. About the SFO airport, United is the only airline that flies to/from Shanghai. Other carriers that fly out of Boarding area G are:
-Air China, Air New Zealand, All Nippon, Emirates, EVA Air, Lufthansa, Singapore Airlines, and United (from Beijing, Cancun, Frankfurt, Ho Chi Minh City, Hong Kong, London-Heathrow, Mexico City, Osaka, Puerto Vallerta, San Jose del Cabo, Seoul, Shanghai, Sydney, and Tokyo) My point is that to my guess and speculation Shanghai is a decoy leg since there is very little evidence other than crew spotted at Nanjing Road and the teams arriving at the United Int'l Gate area of SFO Airport.