agree with you there. My bet for the "final boss" either be Shanks or Black Beard. Because I have a really bad feeling way before during the pre-time skip arc, that Luffy's gonna fight Shanks for the "King of the Pirate" title and return the hat (since it was a promise). BUT that's just my theory, so yeah.
Yes for the Shanks part. I said this for years.
Everyone keeps saying Shanks is gonna be final boss, but I only see it happening if he is controlled by Imu or smthn. Though i do think he might have a full on spar with Luffy after the big fight as a sort of epilogue to see who's stronger.
Might turn out different if there ends up being an actual race for the final island or something though (which speaking of, we still need to knw wtf roger said to Shanks at the end)
Watch this arc end with Imu going back to his little hideaway to recover, and Luffy and the others also stretched to their limits.
I simply don't see him being fully beat this early, regardless of whether he's the "final boss" or not. The others seem like they're fair game though.
There also might be something happening with the Rain Goddess too imo... Maybe gain temporary sentinence like someone commented a few chapters ago?