Why do you go on with your light/draenei/naaru theories when it says in game that it's got nothing to do with it?
Beledar is a crystallized soul fragment of the worldsoul. I think it's pretty clear that it's not a Naaru ship or a portal for a draenei from another timeline AND another planet, since this has been denied.
It was a good idea, a very good one indeed (Naaru ship, not Yrel), but too obvious. It's much more complex and mysterious than that, and I really like the direction it's taking.
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The radiant song comes from the worldsoul. Anduin wonders if it came from Beledar at some point, as he feels a similarity to it (normal, since it's a soul fragment from the worldsoul).
Anyway, from our point of view, we've known it since the cinematics, but the WoW characters haven't. That's pretty bad writing.