Turbine's published another developer diary, this time focusing on some of the changes required with Book 14:

Book 14: The Ring-forges of Eregion "...brings with it a number of great new additions and features, but for those of us heavily invested in the storyline, one of the most exciting developments is also one of the longest-awaited: the Fellowship will finally depart Rivendell on their errand of secrecy."

You can enjoy reading about all the effort at the official site, here.