SC would have to come up with an unbelievable offer for Boeing to consider going there. It'd be like poking a hornet's nest with a stick..drive the IAM nuts..not worth the risk..
Dallas has an old Air Force base right in town that the Air Force gave to the city and isn’t being used right now. The city is trying to sell it. That would also be a good choice.
A few more bombers built in KS than in WA in WWII, but over 80% (6,680) of them were B-25s from the North American KC, KS plant (very little aviation workforce in the KC region nowadays)... Boeing’s only production in KS for bombers was 1,644 B-29s in Wichita. Still a possibility, but neither have the deepwater port that Boeing would highly prefer (especially after landing a Dreamlifter a few miles North of McConnell AFB in Wichita this week ;)