Just a couple of days ago, Blizzard poster Tigole announced that the last instance at the Hellfire Citadel, Magtheridon, was being evaluated.

The reason for such is that the Blizzard's internal raiding team was able to successfully beat the boss and they felt that the encounter was properly balanced, but there have been so many issues regarding it on live servers. Players have been raising several concerns like the encounter requiring too many consumables and potions. (Not everybody has the time to farm.) Tigole added that they will be making "minor tuning adjustments" as the encounter is not supposed to be more difficult than Serpentshrine.

After the announcement, Tigole came back saying that a hotfix was made to fix a bug with the Hellfire Channeler. Apparently, the Channeler's Dark Mending spell was healing "more than intended." He clarified that the hotfix was not a tuning adjustment but rather a bug fix.

Interestingly after the hotfix, a Horde guild on Magtheridon EU  - Nihilium - downed Magtheridon and completed the attunement quest to enter the Eye.