Here is what I see them doing, like they did with flight ops.
Open or move the center to another region.
Offer the employees the jobs if they move. The younger (cheaper) people will most likely move, while the older (more expensive) people are more established, and will not.
That way, you have the trained people without the expense.
I dont really think that, given Boeing's different locations of design and manufacturing, that anyone can say that there is an inferior product coming from a particular location.
If anything, the facility in SC is the most modern, is not constrained, and incorporates the lessons learned from the other assembly lines...typically that means a faster, more efficient line (coupled with motivated workers) would appear to be a very positive move.