Among other mechanics in the World of Warcraft, one that many players learn about very quickly (and painfully) is the matter of aggro/threat control. This is an especially important detail to remember, especially if your party happens to be engaging the likes of Kil'jaeden. 

With that in mind, Blizzard has recently addressed an issue that affects Kil'jaeden's Soul Flay ability, specifically the rules that govern whom it will target. As Daelo over at the WoW forums elaborated regarding the new hotfix:

Soul Flay now targets the player with the highest threat against Kil'jaeden, regardless of the distance between the player and Kil'jaeden. The normal threat buffer that prevents a creature from changing targets to someone outside of melee range does not exist with Soul Flay. Soul Flay will still not target a player who is immune, however.

For the guys who've been planning to take down this Eredar, consider this your cue to start making the necessary adjustments to your raid party's strategy. On the plus side, this new mechanic should make this boss just a little more predictable, hence easier to take down. Of course, it all boils down to your group's own skill. Good hunting, and be sure to visit again in case of any further updates.