The final villain is the new Kuma, who arrives when you think it is all over.
Actually, i believe Story's Kuma is gonna be Death itself
Can't call it Final Villain because Luffy won't face it, it's more like a Test, rather than a Final Fight
The reason i'm saying this is because of what Kuma ended up doing,
The whole concept behind Thriller Bark is that it was like a Nightmare & They couldn't face the Dawn unless Moria was Defeated
Who ended up taking all Zombies with him, ending the Long Night & entire existence of Zombies (For that Arc)
So it's like They woke up, like the Nightmare didn't exist & They can pretend like it never happened,
But then Kuma shows up like a Judge, like He was telling them that you can't just wake up for Free, you must pay for what you have done
The Nightmare needs to remain with someone (It's like imagine We all had a Shared Nightmare & when We finally managed to wake up from it, only one of us continue to suffer from it, while others were able to forget)
It's like someone needs to be the Dreamer,
That's when Zoro offered himself (Sanji also tried)
And what Kuma gave him? All of Luffy's Pain/Damage from Thriller Bark Arc.
After Sanji saw what happened to him, it looked as if only Zoro experienced Thriller Bark Nightmare, He ended up as the Dreamer
And He said "Nothing Happened", which matches with what i said, Thriller Bark Night was like just a Dream, it was only Real for Zoro
So what's the only thing that matters in Thriller Bark? Meeting Brook which happened "Before" They entered TB, and his Recruitment/Backstory/Song ... etc which also happened "After" Night was Over
In other words, Story's Brook is who Luffy bonded with before his Journey started, it was Shanks, One Piece Manga is his Story Arc.
The Whirlpool that took Luffy as soon as He started his Journey represented the Start of Nightmare, just like when Thriller Bark "ate" SHs.
(So it's possible that this Whirlpool Guy is like Tararan of Story, his Role is to Capture & Deliver People to Final Villain so that He uses his Power on them whatever it is and use it to keep the Nightmare ongoing)
Once Final Villain is Defeated & One Piece can finally be enjoyed (Just like Dawn).
Death will appear that isn't glad with what happened, demanding Luffy's Life
This whole One Piece Story is inspired by Movie "Adventures of Baron Munchausen"
Whether it's the War itself, the Adventure, Celestial Dragons, Whirlpools, Elbaf, Poseidon, Death, Blackbeard Pirates, the Ending
I believe OP Ending will make everyone question what was True & what was a Lie, exactly like that Movie.
In short, the events themselves in One Piece are "Lies" but aftermath or results are "True".