EU guild Nihilum released a kill video of their world first Illidan Stormrage kill a few days ago.

Having watched the video, it seems to have 4 distinct phases. In phase 1 Illidan is tanked and moved out of the blue fire explosions on the ground. He places a debuff on seemingly random people that does significant damage and spawns two adds on them which need to be dealt with quickly.

Phase 2 occurs at around 60%, where Illidan takes to the air and begins shooting fireballs and waves of blue fire down at the raid. His two Blades of Azzinoth spawn two giant fire elementals which need to be tanked and killed before he returns. The abilities they use are hard to see, but it looks like there is significant damage going out to the entire raid during this phase.

Phase 3 is a rehash of Phase 1 but at certain points Illidan goes into a demon form and is tanked by a warlock. He also randomly stuns around 5-6 raid members and sends slow moving mobs after them which presumably need to be killed before they reach them.

Phase 4 seems to begin at 30% and is heralded by the entire raid getting put into "Shadow Prisons" that stun them while Maiev Shadowsong arrives and begins to assist the raid. It looks like the same things occur during the final phase as during phase 3, including the demon form. It looks like Maiev drops traps that the tank must drag Illidan over, which bind him to the ground and perhaps weaken him allowing for extra damage.