Or it could be the reverse: the taint is the result of a screw up, created by the separation of the elves from whatever magic made them immortal. It's an independent source of magic, it makes people functionally immortal, and it can sustain things.
You know, you could be onto something there. Since lyrium is the embodiment of magic, it is possible that its creation (since there's no proof that lyrium has been around pre-Veil) was a result of the elves losing their immortality since we know that both their immortality and their proficiency with magic were simply due to being elven. Since the Black City is seen as the source of the taint and there's lyrium present both in the physical world and the Fade, it's entirely possible that the taint corrupted the lyrium it came into contact with in the Fade and was then transferred to the physical world that way. Since the only sources of lyrium in the physical world are underground, the taint could easily have spread to whatever creatures came into contact with the red lyrium, soon spreading to dwarves and other races on Thedas before eventually becoming the massive darkspawn horde that we know today.
But then, we do know that Cory went to the Black City and the First Blight came around not all that long after he and his crew returned, so maybe my theory is better suited to be a theory on the origins of red lyrium. On second thought, that makes more sense.