Looks like Apple isnt completely opposed to making running production changes, they are switching the type of ram in the 64/128GB models.
http://www.dailytech.com/Report+128...pt+Apple+to+Abandon+TLC+NAND/article36854.htm
"BusinessKorea earlier this week surmised that the problem stems from the triple-level cell (TLC) NAND flash used in 128GB models of the iPhone 6 and iPhone 6 Plus. Today, the same publication stated that Apple will reportedly switch from TLC NAND to multi-level cell (MLC) NAND going forward for in the production of both the 64GB (users have reported similar issues with these devices, but to a much lesser extent) and 128GB iPhone 6/iPhone 6 Plus smartphones."
http://www.dailytech.com/Report+128...pt+Apple+to+Abandon+TLC+NAND/article36854.htm
"BusinessKorea earlier this week surmised that the problem stems from the triple-level cell (TLC) NAND flash used in 128GB models of the iPhone 6 and iPhone 6 Plus. Today, the same publication stated that Apple will reportedly switch from TLC NAND to multi-level cell (MLC) NAND going forward for in the production of both the 64GB (users have reported similar issues with these devices, but to a much lesser extent) and 128GB iPhone 6/iPhone 6 Plus smartphones."
