Luffy eating the Nika fruit opens up the possibility that he was entitled to the One Piece from chapter 1.....which is kind of annoying? And it opens up a lot of weird questions about why the Nika awakening isn't even hinted for 1000+ chapters.
Naruto being the Asura reincarnation is still probably worse, since it really does come up last minute, and imo the connection with the Uzumaki to Asura through the Senju is like, hilariously forced lol. Also, I think explicit reincarnation when introduced so late is a bit much...