Unfortunately, this aspect of the Arakkoa was quickly forgotten. An intriguing side story to the race which could supply another facet of understanding to the Light simply fell apart. It broke down to 'oh man the Arakkoa are TOTALLY evil' nonsense and we were doomed to encounter them in absolutely every zone and still manage to learn nothing new about them. Everything you need to know you learned in Lower City. Terokk is a bad guy who was worshiped as a hero. The Arakkoa are dark and naughty. The end.
Terokk finally makes his appearance when you hit level 70, as a summonable boss in Skettis. The ultimate villain of the race you battle in four out of Outland's seven zones is nothing more than a summoned boss tied to a Silithus-esque grind. Who in the world enjoyed farming hundreds of pages and pieces of clothing off of Twilight Cultists? Nobody. The resolution, which was a disappointment before we even reached it, broke down to Silithus 2.0. There's a very good reason everyone and their cousins hated Silithus. Terokk doesn't even give any compelling reason to summon him. His loot, for the most part, isn't especially powerful or interesting besides the arakkoa disguise.
What would I have done differently? Lower the Arakkoa presence in many of the zones. Terokkar, fine. Blade's Edge? Ehh, okay. Hellfire Peninsula? No. Shadowmoon Valley? Not unless you're going to expand on the Old God-esque storyline that ended in a fizzle.
Add Terokk as a summonable boss inside of Heroic Sethekk, just like Anzu. Maybe Ikiss could be guarding a shrine to the 'hero', or is using his precious trinkets to gain the power of Terokk, and killing him accidentally frees Terokk himself. Perhaps place Terokk inside of an instance up in Skettis. There's a lot you can do, and a painfully long grind for drops is the worst possible choice.