Nobody has beaten it because anybody who knows the fight to a tee would tell you that is impossible with current gear levels or pretty much near impossible. Those claiming to have killed it are either trolling or are mixing up what HEROIC ELITE means. We beat NORMAL ELITE the first week and somehow got multiple 516 items from a coin. Why? Because it was fucking bugged. Just because you have loot from the heroic elite version doesn't mean that you killed the boss lol.
Kaolon last means your entire raid is taking 150-180k damage every 3 seconds for nearly 4 minutes of the encounter, with 1/2 to 2/3 of your raid taking 120k damage every 3 seconds for the first three minutes or so. The 120k and 150k damage isn't as bad in the first half of the encounter considering you get a 25% haste buff periodically in addition to your entire raid healing 5% of max health every 3 seconds and receiving 50% more healing. Koalon has the most HP and doing him last without the 25% haste buff or this healing buff means your raid is at least going to have to deal with massive movement (because of his solo ability), killing adds properly all the while trying to kill him before you run out of room or healing.
It just makes me laugh when people casually say they killed it. You didn't because it does stupid amount of damage. The heroic elite version isn't mechanically difficult, it's just tuned with incredibly high numbers. At the moment you can probably make your raid designed to beat the enrage or handle the damage, I don't think CURRENTLY it's possible to do both.