The historical conflict since one piece started has always been between Ds and Celestial Dragons
> Existence of the ancient kingdom that has been erased by them
> Said ancient kingdom who had enemies
> And with the alliance of nation creating the land of mariejoa
With Ds viewed as enemies of the gods(celestial dragons)
So because of this, alone i think the final arc will resolve more around the Ds and Celestial Dragons than marines who are more used by the world government in the entire thing(Gorosei using Cp0 behind Akainu's back for a deal with Doflamingo, them using Cp0 to keep tabs on Wano without marines knowing, Aokiji deserting the world government after believing they aren't the end of all, Fujitora doubting the world government behaviour and so on).
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And beyond this, i believe this picture in particular suggest there would be a meeting between Imu, Blackbeard and Luffy
With Blackbeard representing the "evil D" aiming at overthrowing the Celestial Dragons and reign supreme in an era of terror, disliking "boring peace" in MF while attempting to sink everything
With aims at controlling the world
With his behaviour being too evil imo for Whitebeard to realize Roger wouldn't root for him since he'd try to destroy the world and create his era of terror instead of seeking peace.
Hence why i think that overall the
final villain will be between Imu/Gorosei and Blackbeard