With the addition of Gun'drak, Akali's platform in Zul'drak has been upgraded. He is still chained and tortured by the Prophet of Akali to gain powers to fight the Scourge, but the platform itself is now see-through.
After exploring the dungeon, it is clear, that Akali's platform offers a peak into the central part of the instance. The level 76-78 instance has 2 separate entrances close to this platform, both starts by taking players down below the surface using an elevator. Here they shortly come across the previously seen part where they must solve a puzzle to unlock the last boss, Prophet of Akali.
This makes us wonder, what does the currently unused main fortress of Gun'drak hold? Due to its massive size my best bet is on a raid instance that would be introduced after Naxxramas, Nexus, Chamber of Aspects and Ulduar or a second dungeon wing for high level players.