Heavensward Art (Potential Spoilers)

[Nalien]

You kinda contradicted yourself by saying the last bench had no unique models and that the last bench included Ifrit

Let me clarify, I mean the models we saw in the Benchmark were not unique to the Benchmark. The Ifrit we saw in the Benchmark was the one we got in game, same for the Mindflayer.

That goes for gear as well actually. The only things in the Benchmark we saw that were unique to the Benchmark were various scenarios (Ifrit FATE) and various scaling up of enemy sizes (giant enemy turtle). That's it. All the models for enemies and gear that were in the Benchmark were the same as what we got in the game. Nothing was changed. I see no reason the same will not be true for Nidhogg here. There should be no models in the Benchmark which are unique to it, they're all taken directly from the game to test performance, as such the Dragon thought-to-be Nidhogg should look exactly the same in game as he does here, though perhaps with some scaling changes; As such the fact that he is missing an eye in the Benchmark is as good a proof that he will in the game. So we have a Dragon model missing an eye, and two promotional art pieces with two different Dragons missing an eye.

Why would they show us such an important encounter such as Nidhogg so early into the expansion?.

Why not? We took Gaius and Ultima Weapon out in 2.0, I see no reason why we similarly wont be taking out Nidhogg in 3.0. 3.1+ could be based around the other Celestial Dragons or saving the Scions or who knows.