There is almost no lore relating to the 5th race, but I believe it does still exist and is not the Taken. I’m going to speculate that Forsaken DLC 3 “Penumbra” is going to be our first real hints to the 5th race. Our best hint at the Darkness so far are these notes from Cayde-6 in his Treasure Island book that came with The Taken King:

There's no bounty. No Hive. I'm out in plain sight. Sky is torn open and there's nothing and nobody left in this ruined world but me and the boiling shadow all around. Whatever it is hits me before I can level my gun. Doesn't matter. Tendrils of pain crawl over my splayed fingers, my outstretched arms, my shoulders, my neck, my screaming mouth as it consumes. I'm being enveloped. Everything is wrong. Primordial. My systems go sideways. All but my sensors. It wants me to witness this, the world.

There’s also this from Ghost Fragment: Awoken 3. I believe this has something to do with the initial transformation of the Awoken when the Darkness attacked:

Fear. That’s the only vivid memory left in me. It’s the moment when my fear was so thick and urgent that I gave up breathing. I stopped pretending to think. How I remained on my feet was a mystery, because the terror was bearing down on me, like a mountain about to crush my soul.

But I have to ask, “What was terrifying me?”

Darkness ruled the sky. The world around us had shattered, and it seemed vanishingly unlikely that we would outlive this one awful day. Yet the fear didn’t come from the surrounding mayhem and despair. The source was inside my skin. I was utterly terrified of my own awful nature.

That’s all there really is for now, but given the Dreaming City and this original idea about the Awoken’s creation from the “Awoken” Grimoire card...

It is said that the Awoken were born in the Collapse, descended from those who tried to flee its wrath. Something happened to them out on the edge of the deep black, and they were forever changed.

...I’m sure we'll learn more relatively soon.

Questions:
1. Do we know that the fifth race is the Taken?
2. What do we know about the triangle ships?
3. Are those ships related to the Taken (based on the triangles on the fifth race card)?

• The Dream sequence implies the triangle ships are the Darkness, and it looks increasingly like the darkness encompasses all the possibilities:
  
• The Pujari Position describes the Darkness as a force with both physical and moral presence, an actualization of evil. Pujari art depicts the Darkness as a great storm, or as a change in conduct, a corruption that emerged from within and poisoned the Golden Age.
  
• Saint-14's Position argues that the Darkness was an invading armada, an alien force of incredible - but tangible - power. Some adherents believe that this armada sprang from species rejected or discarded by the Traveler for their sins.
  
• Ulan-Tan's Thesis considers the Darkness a necessary symmetry to the Traveler in a cosmic balance. In this view, the Traveler's goodness led it to sacrifice for others, and it is up to us to return this goodness by healing the Traveler.
  
• The Monist Position, or the Deflationary Position, considers the Darkness as a technologically sophisticated force, perhaps a post-Singularity intelligence. Adherents invoke information theory or contend that the universe is a simulation, allowing advanced intelligence to gain weakly acausal powers by bending the rules.
  
• The Acataleptic Clause claims that we are intrinsically unable to understand the Darkness. In many respects this belief parallels the Praxic Creed, which suggests that we should stop worrying about the nature of the Darkness and focus on resisting and defeating it.
  
• Certain positions - often labeled heretical - imply that the Traveler itself triggered the Collapse, or that it knew the Darkness was coming for it and hoped to use the Solar System as a sacrifice or a proxy army. The Binary Star cult is one notable example. on the grimoire card:[/i]

The Taken are made by the Darkness, and may act as it's foot soldiers. They are were thought to be the 5th race early in D1 because of their ghostly aura and large glowing head spots seemed to match the 5th race image in the old concept art. However, that may not be the intent. As a "race" made of those kidnapped from other factions, they instead may be a filler concept, and we have yet to see the true form of the Darkness and it's "formlessness".

It appears however that their arrival will have to wait till D3, since D2's expansions have to deal with wrapping up the Cabal arc and expanding on the Dark age lore.

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