Honestly, I don't think the Gorosei will primarly stay as Imu's companions or at least not in the way how they were shown in Egghead Island, given how Imu has the ability to summon and revive demon armies. We might be getting demon versions of characters who already died. Iirc, @Elder Lee Hung even came up with the theory that Imu - or the being behind Imu - might summon the 20 ancient kings of the kingdoms which will act as his real companions.
I’ll be very surprised if, after the slow burn build up of the Gorosei over years finally going into overdrive to reveal that they are practically immortal demons, that Oda then tosses that aside to reveal there are… more immortal demons but older immortal demons. Or dead immortal demons, or whatever.
Like, in this theory is Zoro not fighting Nasujuro, but instead is another Ethanbaron that rises from the dead and fulfills the exact same role, with the only difference being one is centuries old, and another is even older? Or is he fighting both, which is even more baffling.
Replacing Saturn after he got to be main villain for an arc specifically with Shanks’s father to set up the Figarlands as major EoS players is one thing, replacing the rest with characters who are practically the exact same before the others really get to do anything is a different story.
Who says Mars will be Sanji's final opponent? An admiral could be his final opponent and that's more than enough considering that they are viewed as complete monsters in the One Piece world.
It’s very unlikely that an Admiral becomes Zoro or Sanji’s final opponent. They are tied too closely with Akainu as his equivalent of commanders, and Akainu has no shot of being the final villain.
What I am saying is that Sanji's ceiling got huge upgrades. Furthermore, Roger would destroy Mars but how would it look with Demon Mars? Looking at Demon Brogy and Dorry - if both of them are on a completely different level compared to their "light peers", it would make the Gorosei even far more powerful.
I'm certain that the Gorosei are not in their demon form because they'd have horns and wings. I guess that'll happen as well.
It makes more sense that the Gorosei’s transformations (and Shamrock’s sword) are part of their own contract with Imu for immorality. And that’s why they got the strange introductions that don’t mention DFs, unlike with Gunko, Sommers and Killingham. Dorry and Broggy’s is a generic devil transformation that’s main purpose is to force a good character (white) into a bad (black).
The Gorosei are unlikely to have needed to be forced, and they already have their own unique demonic transformations, as opposed to the giants getting generic devil ones.
Like, is Peter supposed to become a flying bat worm with horns?