These posts about the naaru are mainly speculative. I hesitate to use the Tinfoil Hat title, because I'm not postulating that they're secretly evil or anything. But the fact remains, we know very little about the naaru. We don't know where they come from, how long they live, if they can enter their Light/Darkness cycle indefinitely, if they ever die naturally or even if they can be really killed. The only one we've ever defeated in combat ended up part of the Sunwell, and who's to say what he's doing in there now? Is M'uru still alive in the Sunwell, or did his mind die with Entropius? We currently have no way of knowing.
We know that despite what we experienced in The Burning Crusade, for the naaru, entering the void phase of their existence is an exceedingly rare and perilous event, at least according to the Ask CDev threads. It is this unknown quality that fascinates me about the naaru.
As we discussed last week, the Ata'mal Crystal that Velen used to create the barrier of Light and hold off Archimonde and Kil'jaeden's followers was an ancient mystery of his people. We don't really know where it comes from or if the naaru gave it to the ancient eredar or if the eredar constructed it somehow. What we do know is that at some point in the distant past before Sargeras came to Argus, the eredar and the naaru had some form of contact. This implies that the naaru may well predate the Titans. What we do know is this: Somehow, in some way, the eredar and the naaru met, and the Ata'mal Crystal was left in eredar hands until Velen came to call upon it for guidance.