It's likely that this downtime is for working out a few kinks with the Midsummer Fire Festival. Kisirani confirmed earlier that there is a problem with the Striking Back quest for those under level 65, so it's likely that these rolling restarts will institute the hotfix to that problem. In addition, there's been some rumors that Lord Ahune's Normal and Heroic loot tables are not properly separated, so it's possible that this will fix those issues as well.
Speaking of Ahune, be sure to keep your eyes glued to WoW Insider today. We're writing a complete loot guide and a strategy walkthrough for the new holiday boss as well speak. You can also check out the Midsummer quest walkthroughs we already have set up -- they're perfect reading material for the downtime. Happy reading, and we'll see you on the other side of the restarts.