Some idle speculation.
What if there's more than just Zodiark and Hydaelyn? Both Omega and Midgardsormr are referenced to have come here from another place and Midgardsormr made a pact with Hydaelyn implying they may be more equal than most other beings. Is it possible there could be other beings like Midgardsormr who could communicate with us if they chose? Things seem to make a "little" more sense if we assume its not zodiark speaking but some other powerful entity.

Another possiblity could be not another singular entity but several acting in concert? If a group of people with enough crystals could reach across the dimensional barrier to summon a primal, couldn't that group try to summon the WoL too?