OH MY GOD YES YES YES
TIDUS AND YUNA BREAK UP YEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEES
Also, I don't hate the idea of Sin coming back. I know they thought the defeated it permanently, but it could be really interesting for characterization. I mean, you could explore the theme of hubris and the fact that despite Sin being reborn eternally, they thought they beat it.