From the last WoD plot line, we know that Hydaelin isnt in complete control of the influence light has on the world
Its not necessary for sonething to corrupt her, only for the balance to tip in her favour.

The trailer seems to imply some kind of time travel, it implies its been 'years' since we fought Zenos. Seems like the voice we've been hearing is an alternate reality WoL (us) from the future, attempting to 'rewrite history'.