Alright, I would like to premise this theory first with a statement that I always thought that Luffy and his allies would ultimately clash with the World Government and the Marines at the final war (excluding the final battle with Blackbeard)
But, some developments happened along the way and kinda made me think of possibilities so, I would get this out of the way immediately:
The Marines (at least some of them) would breakaway from the World Government and execute a Coup d’Etat.
Now this faction would be very different from the Revolutionaries.
The Revolutionaries wanted to overthrow the government and got no problem affiliating themselves with outside forces like Pirates.
But the Breakaway Marines (we will refer to them as X-Marines) are the guys who still detest pirates, the same way they detest the World Government.
There are several instances in the manga why this thought came to my mind.
First is the apparent disappointment of the Fleet Admiral over the decision of the World Government.
Second is the desire of Admiral Fujitora to defy the government privateers called “Shichibukai” system and his obvious disdain for the World Government.
Now, the other reasons I have are just a speculations, but I believe I got good grounds for it..currently in Zou arc, some parts of Sanji’s backstory had been revealed, and it was said that this “Vinsmoke Family”, which Sanji is a relative of, leads a group called “Warhouse / Germa Double Six”
Now with the involvement of Capone “Gang” Bege, who obviously had been inspired from Al Capone, a famous Mafia Leader, it would be fair to assume that Capone was hired to bring the news to Sanji by another Mafia Group.
Which is kinda confirmed in a way because they are said to be a “Family of Assassins”, well either way, moving on….
With “Germa 66” name as well, I would assume that Oda used this name in order to reference a group/organization from the movie “Kill Bill”, by Quentin Tarantino (Oda loves Tarantino Films)
The Crazy 88, which is led by a Mafia Leader / Underworld Leader.
(wouldnt be surprised if the Vinsmokes hide their faces like this to hide the eyebrows. LOL.)
I’ll dive into this topic in another theory (and Germa 66 connection to a card game), but lets just say, the head of Vinsmoke Family lured Sanji into doing what he wants by using someone Sanji loves as a bait.
The point i’m trying to make (which is kinda confusing coz I rambled on) is that the Vinsmoke Family is a Mafia Family.
I’ll just get straight to the point.
Each of the Gorosei leads their own organizations, so that makes it 5 organizations including the Germa 66 and Cipher Pol.
Simply said, in the game of chess, those 5 organizations are the real “guys” of the World Government.
The Marines?: Pawns, disposable pawns who always get fronted in battle and dont know the real “identities” of the World Government, especially the Gorosei.
So I believe some Marines would breakaway from the World Government and start a new faction.
So in the final war, we have:
1. The Strawhat Pirates and its Grand Fleet.
2. The Blackbeard Pirates and its Grand Fleet.
3. The World Government (Science Division, Germa 66, Cipher Pol etc.)
And yes, I don’t believe the Red Hair Pirates and the Revolutionaries would be there for the Final War…
*Theory by beck