Even though they haven't announced which site will benefit from the rate increase, I fully expect that Boeing South Carolina (Charleston) will see most if not all the increase in the rate of the 787. This rate increase is being timed with the need to produce 787-10 aircraft in sufficient quantities by 2017 which is when Boeing expect to start testing the double stretch of the 787. I can also see some interim production increases (to 11 in 2015 and to 13 in 2017-2018).
This announcement also will fuel the discussion as to where the 777X will be built. With JALs announcement that they will buy the A350, there is increasing outlook that Boeing will build more of the new large jet outside of Japan (even if ANA orders it). I believe that Boeing will build this airplane in Everett and assuming that the future 787 increases are built in Charleston, I can see a stronger case that the final assembly of the 777X will take place in Everett.
From Boeing's press release:
During the quarter, the 787-9 completed first flight. With the successful launch of the 787-10 and continued strong demand for the 787 family of airplanes, the company intends to increase the 787 production rate from 10 to 12 per month in 2016, with plans to increase to 14 per month before the end of the decade.