Alternate universe where in X/Y Lysandre was actually the champion and was framed as the leader of Team Flare by Diantha, the real leader.
Pokemon Z is made as a sequel to show that Diantha is back and is planning to use Zygarde to make the world "perfectly balanced". Things like Ash-Greninja and Zygarde forms are introduced here. Sun and Moon have less of a rush put on them, which inevitably leads to a rise in quality.
Whether or not ORAS is still a thing is up to you.