Daelo is saying over on the forums that the Kael'thas event is bugged. After a player reported that the shield (one of the magical weapons that you first have to defeat and then can fight Kael'thas with) has tons more health than expected, Daelo confirmed that if Kael'thas resurrects his advisors while weapons are "alive" their health will be increased, making the fight much harder and throwing most guilds off of their pacing.
So if you're headed to Kael'thas this week, beware. Unfortunately, Blizzard says they can't hotfix the issue, which means it'll have to be fixed in a content patch. Fortunately, however, 2.2.2 is due this week, so if Blizzard can sneak it in yet on that one, raiders will be able to take Kael on as of Tuesday. If 2.2.2 is already too far along in the process for the code to be added, however, Blizzard will either have to create a patch just for this fix (2.2.3), or wait until 2.3 releases (which could be a matter of weeks, severly hampering guild progression past Kael).
We'll have to wait and see what they do. This is a confirmed bug, so hopefully we'll see a fix for it with 2.2.2, hopefully on Tuesday.