The gate to Illidan cannot be opened until the Council is dead.
I do not know if it is possible to sneak past Shahraz.
The gate to Shahraz requires Gorefiend, Gurtogg, and Reliquary all cleared.
I don't know if Akama is tied to that mess as well.
The gate behind Supremus cannot be opened until Supremus is dead.
Attempting to run past Naj'entus will cause him to throw impaling spines at you while running up the tube to Supremus. This mechanic (supposedly) is what causes the graphical glitch players see when they are running up the tube and suddenly get a bunch of missed needle spines in their combat log. The attack only misses because Naj'entus is, well, dead.
-Splug
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(Usually) Prot warrior:
http://www.wowarmory.com/character-sheet.xml?r=Illidan&n=Splug