Nah they can since -10 is wholly made at CHS and cannot be flown to Paine. That will be the study outcome, do it all at CHS.
This also strikes me as the most likely scenario, but another possibility is they expect demand to ultimately recover beyond what Charleston can produce with the existing facilities. If they believe that will be the case, they might choose to keep Everett running rather than invest in enlarging Charleston.
Instinctively, it doesn't seem like consolidation to Everett only stands much chance, but I think it will be looked at anyways, because the Everett leadership team is likely to insist on it out of self-interest, and a few thousand labor hours of analysis is cheap in the grand scheme of this industry (especially if projects on hold or slowed down are freeing up more people than have been laid off).
I also think it is worth mentioning that the Machinist's union has a notice to members on their website indicating that they have been led to expect Boeing will soon try to negotiate concessions from them. Asking for concessions only make sense if Boeing has something to offer in return. On the other hand, such offers could be security for the 737, 777X, or even NSA/NMA instead of the 787.
As we all know, that didn't go too well and Boeing ended up having to buy out Vought and their Charleston factory for $580m in 2009. So it ended up with Boeing building their own 787 fuselages in Charleston. The -10 came along later and its fuselage was too long to fit inside the Dreamlifters, so the second production line came into being.
Boeing bought half of the Vought factory in 2008, and the other half in 2009, followed a few month later by the Charleston final assembly line announcement. The -10 was officially launched in 2013, so I presume there was some leeway defining details like which barrel to lengthen or whether to use a fully separate plug through at least 2011. The Charleston dependence of the -10 was disclosed in 2014. It is possible that Boeing planned an assembly line next door to Vought all the way back in 2003 when the 1st tier suppliers were announced. However, they had much loftier ambitious originally for the throughput of the Everett line, and the motivation driven by the 2008 strike was clearly not a factor at that time, so I don't think it was considered necessary.
Considering those factors, my assumption is that their baseline plan in 2003 was that the -10 stretch would be implemented in a manner compatible with the Dreamlifter. Later on, with the Charleston assembly line already in existence to make up for the production issues, they ended up not being limited to plans that included moving the -10 center section cross-country.
Also, I think we might be collectively misunderstanding the constraint somewhat. I was confused and thinking the long center fuselage section was solely a Charleston product. Here is what I just researched to find clarification for myself:
Charleston does not fabricate the barrels for the 787 center fuselage section. Those come from Alenia (sections 44 and 46), Fuji (Center wingbox), and Kawasaki (section 43). Those sections are transported to Charleston, sub-assembled together, stuffed and painted, and then moved as one piece to the Everett or Charleston final assembly lines.
Therefore, if Boeing were going to consolidate the 787 back to Everett only, they would have to build at least a -10 center fuselage assembly station in Everett to join the sections and install the systems that need to be in place before final assembly. Optionally, they could include enough capacity to make the -8 and -9 center fuselage assembly, too. They would not have to install the composite layup equipment, autoclaves, trim machines, and frame installation jigs, as those were never located in Charleston (except for the aft fuselage)
AFAIK, it's not impossible that manufacture could be moved to Everett, but it would presumably be horribly expensive.
For a single section using already designed tools and equipment, it would be significant, but not horribly expensive. My wild guess is over $100 million, and 18-36 months lead time. The time to implement and juggling space with the 747 shutdown could actually be a bigger problem than the cost.