Ultra Sun and Ultra Moon will end with Necrozma revealing its true form (Psychic/Dragon, fusion of Holographic Solgaleo and Lunala) and causing destruction in the Pokémon universe. Being the Omega Pokémon, the universe will be reset, no more multiverse, instead there will be 2, a singular mainline universe starting with Generation 8 being a reboot and the second universe being simply remakes of previous games so that players will get the best of both worlds (The original 800+ and the new 800+)