Around October, Boeing will reduce the number of 787 airplanes assembled on the surge line by 2 aircraft/month and reallocate 1/month each to 40-26 and the North Charleston line. 40-26 will assemble 5/month and North Charleston will assemble 4/month while the surge will still assemble 1/month. It has been Boeing's plan to use the surge line as a temporary line while they got the North Charleston line up and running and increasing the production rate from 3/month to 10/month.
I believe Boeing has enough confidence in the North Charleston facility to to increase its production rate early. Boeing is supposed to increase the North Charleston rate to 5/month in 2016 but it appears this may happen sooner than expected. I do believe that in 2016 Boeing will shut down the 787 surge line reallocate the lone aircraft on that line to 40-26 and then when they ready to up the rate to 12/month, assign 1 each to 40-26 and 88-30.
The surge line is planned to be used for final assembly of the initial batch of 777X.