Just a thought - we're assuming that Zenos is going to absorb Zodiark now and be the final boss, but what if it went the other way? Zenos is so confident he can do this, somehow unseals Zodiark, goes to do whatever it was he did to Shinryu.... and Zodiark says "hah, puny mortal, you seriously thought that was going to work?" and overwhelms him. And now we suddenly have a uncontrolled Zodiark incarnate on our hands.