Just imagine if Sasuke gets another power up by some guy(probably of otsutsuki clan) which makes him stronger than Kaguya but Sasuke won't be able to control it and after that he attack 5 nations It's because after a deeper thought his mindset change from what it was after his fight with Naruto and he thinks that the world would be better if he had become Hokage(Probably after seeing Naruto failures of bringing peace like ,Momoshiki and Kawaki stuff) Now let's imagine that since Boruto will be the one to Defeat Kawaki,He stands in front of Sasuke as a threat but then Naruto says that Sasuke is his responsibility then Naruto will be back as a main Hero and they could make Naruto part 3 Where Naruto gets defeated by Sasuke and Boruto somehow able to rescue Naruto from there and Sasuke finally become Hokage and Naruto& Boruto lives in shadows and train themselves to Defeat Sasuke in next fight series 3 will focus on there lives when they are in shadows