At that point in the timeline, most of the business is done on that world because the main threat has ended. That's as far as I'll say so I don't spoil much. As such, once we're free to explore other worlds, in compliance to your wishes (and possibly others) it won't have to be the main one to visit any longer. I would like to spend a lot of time in that world because it has a ton of stuff to explore, but that can be for the stuff taking place before the end of that huge plot arc on the planet. Sounds good? 

For a huge war across many planets, I do have the Ekkren, monsters created by the Archetyp Gods. Maybe with the world no longer closed up on it's own, they're free to travel to other worlds, thus creating a huge problem all around the multiverse that must be stopped. There could also be some Archetyp Gods (who are also free) to lead these armies and take over everything. They can ally themselves with whatever evil armies are in canon with said planets we are visiting.