How about a scenario where Akainu believes both pirates and WG are pure evil and need to be eradicated?
I don't think he'll immediately join the side of the pirates by killing the Gorosei but the final war will include an all out war between all forces, fighting each other. Maybe the navy WILL betray the WG soon but they'll still do their own thing - after all, Akainu showed his determination to eliminate the emperors.
It’s a tale as old as time. I’ll drop my prediction:
So there is actually no real amount of evil that Akainu can discover that will make him betray his ideals. This would make Akainu look indecisive and foolish, like he just supported the WG because he was ignorant but flips sides as soon as he has enough information.
Like when Bellamy found out Doffy used him, Bellamy still supported Doffy because Bellamy refused to betray his own ideals. This makes Bellamy seem principaled/full of conviction, it’s an admirable trait in a way and that’s how Oda tried to portray Bellamy.
Akainu will be similar. When he learns that Imu is an evil demonic overlord, he won’t immediately betray his ideals. He will stand fast to absolute justice because he is a man of conviction.
What
will make Akainu betray his ideals is if:
1. Imu tries to kill Akainu personally
2. Imu tries to kill someone Akainu cares about
I suspect that this is the purpose of Akainu’s daughter Hibari. What Akainu doesn’t realize is that the WG plans to destroy the Marines along with the rest of the world in order to completely erase this era of history and start again. I suspect Oda will write Akainu into a scenario where he will be forced to choose between watching his daughter die, or betraying the WG. And I think in that scenario is when Akainu will betray the WG.
A good example of a trope like this is Darth Vader. Darth Vader didn’t betray the Empire until he was forced to watch Palpatine torturing his son to death. That was when he finally flipped and killed the Emperor. And we know Oda is a fan of Star Wars and used it as inspiration when he was writing early OP.
So yeah, effectively Akainu won’t betray his ideals until he realizes the WG intends to kill him/kill the people he cares about (the Marines/possibly even his own daughter).
This is how you do character development if you do it right. Pre timeskip Akainu was a raging monster, a fanatical lunatic with no humanity, post timeskip Akainu in the end will be portrayed as much more vulnerable and human. We know Oda likes to portrays pre and post timeskips as “mirrors” of each other, where things are similar but also opposite. Shabondy Kizaru was a dispassionate “just doing my job” Admiral, Egghead Kizaru betrayed the WG and was forced to confront his own humanity as he was forced to murder his best friend.
I also think for EOS Admiral battles, the Admirals will appear much more vulnerable than they did at Marineford. Outside of the Whitebeard moment, the Admirals at Marineford were semi untouchable, dispassionately using OP fruit powers to coast through fights they didn’t really care about. At EOS, the Admirals will have to fight passionately, taking heavy injuries and being bloody/roughed up while having to actually show their passions and use more serious Haki.
Anyway I’m rambling but this is how I picture things.