I know some people have been wondering how Solgaleo and Lunala will fit into the story, and I think the last CGI scene in the latest trailer might of given us a clue. At first, I thought Solgaleo and Lunala were heading towards each other to battle (I wasn't really paying attention to the scenes), but as the last CGI scene shows, they are jumping into a portal together. Now this portal looks a whole lot like the portal UB-01 is coming out of:
So my theory? At some point in the game, we'll need to call upon/awaken Solgaleo or Lunala to help us fight the Ultra Beasts and MAYBE take us to the world where they come from since they're heading into the portal. So, in an interesting twist, instead of the evil team using the box art legendaries for their goal, we use them instead!