Debuff limit will be changed to 16 in patch 1.7

[TheLuminaire]

I suspect the devs were worried about kiting on a raid scale. I think the devs had nightmares of 40-warlock Onyxia raids where all of them do Curse of Doom-DoT-DoT-DoT and run around like headless chickens until Onyxia expires from exhaustion.
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That's exactly the reason; in reality, when this change is implemented, most of the end game contet will get rebalanced again, much like they did when they fixed the "unitended resisting" bug.

Although the 40-Warlock raids are an extreme example, there's definately good reason for the debuff limit.