Oda loves creating new characters so much, that I feel like there's a 70% chance any sort of Knight of God replacement is just someone new that we've never met before.
But, it's still possible it could be someone we know, so who could it be?
Gunko is right here. Technically she's only a Shallow-Sea Contract God's Steel. So, she could get a promotion to a full Deep-Sea Contract. But, I feel like the whole reason that Oda even created the "God's Steel" tier of power was to keep Gunko from being fully "corrupted" by Imu. So that it's a little easier to redeem her down the line. Even though, Gunko can do just as much, if not more than any of the God's Knights we've seen. But, yeah, for purely redemption-related reasons, I don't think Gunko's going to take the 8th spot on the God's Knights.
It also COULD be someone from Elbaph. Imu IS interested in ruling this island after all. And they seem to need someone from this island to act as a "ruler" in order to do that. But, that would require Luffy and the Strawhats to fail pretty miserably here. And I don't know if I see Oda doing that THIS close to the end. There isn't a lot of time for them to redeem themselves for such a failure, even as a parallel to Sabaody. So, I don't think Imu's going to end up putting Dory or Brogy or even Road in charge of this island. But...that might not be the case for EVERY island, read on for more about that.
Failing that, we could get a recruit from the Celestial Dragons, themselves. And the most likely candidate there feels like Saint Rosward Shalria, Charlos's sister. Oda kind of hinted at the start of a character arc with her, with her asking about what the Void Century was during Vegapunk's message. And if Gunko ends up getting redeemed, it'd be nice to get another girl on the God's Knights. I could see her getting a upgrade, after learning more about history. She's a blank enough slate that you could do almost anything with her, but she's also been around long enough that'd it be a interesting enough choice. I feel like Shalria becoming a Knight of God has potential. Plus, we'd get to see how the God's Knight train and gain strength from her point of view.
Someone from CP0 would be a pretty obvious choice, especially Lucci. But, we JUST saw Lucci again. So, would it REALLY be all that interesting to see him get a upgrade, again? Meh, I feel like Oda's already played his CP0 hand for the Final Saga.
Doflamingo...look, Doflamingo's one of the best One Piece villains. But, we already HAVE a pretty obvious "traitor" within the ranks of the God's Knights with Garling. Do we really need TWO people looking to stab Imu in the back? I feel like Garling and Doflamingo would kind of cover a lot of the same ground with each other. So, I don't see Imu being THAT desperate for a new God's Knight.
Enel would be a pretty interesting choice. But, I'm just not sure if Imu knows or even cares about what Enel's up to on the Moon. Plus, personally, I would like the choice to be someone who didn't have a Devil Fruit before, so that they can get a new Zoan/Yokai form.
Weevil I could see getting talked into becoming a God's Knight pretty easy. And he does have the power for it. So, him getting a power boost AND a new Yokai form would be kind of interesting. The thing is, I feel like Oda kind of wants to redeem him, down the road. His biggest sin is just being dumb and being around the wrong people, after all. I feel like Weevil's eventually going to get a happy enough ending, eventually. And would the regeneration powers "fixing" his mind be...problematic? I don't know if Oda would go there. I feel like it's unlikely.
Here's one that hasn't been mentioned, yet. Arlong. Arlong is a classic One Piece villain who really hasn't been seen in literal DECADES. He'd DESPERATELY need a power-up in order to play at the Final Saga level. And becoming a Knight of God would give him that power boost he needs. And as we've seen with Qilingham and Maffey and that giant guy on God Valley, the God's Knights don't strictly need to be humans only. (Unless those all turn out to be Zoan/Yokai hybrid-forms.) The biggest question is, would Arlong agree to join up with the God's Knights? Because it does seem to need to be voluntary. And Arlong, famously, HATES Humans. So, it would be a bit of a stretch for his character. But, I think you could make it work. Especially if this is the only way for him to get any sort of freedom. And that might give Imu the chance to get a foothold in Fishman Island, since Arlong lives there, giving Imu a chance to rule the island through Arlong.
Similarly, if Mosa DOES turn out to be Shirahoshi, then it sounds like something is going on at Fishman Island. So, it would make sense if Imu made someone a God's Knight from Fishaman Island, in order to act as the new ruler of that island in the name of the World Government. So, it might be interesting to see the return of Vander Decken. But, again...Arlong is right there. And between Arlong and Vander Decken, even though canonically Vander Decken is probably stronger, Arlong is the more INTERESTING option. And...I personally just find any of the non-Energy Steroid aged New Fishman Pirates to be interesting enough to even bother mentioning them.
So, if not Arlong, what about another early One Piece villain? How about Axe-Hand Morgan? He WAS a Marine, so he already has a easier in with the World Government. And it WOULD be nice to see the "first" One Piece arc-villain make a big return. But...I feel like no one actually cares about Axe-Hand Morgan. So, it wouldn't be as hype as Arlong would be. It just doesn't feel like the most interesting option.
Here's a thought. King Cobra is dead. And Vivi is on the run with Big News Morgans. So...who's running Alabasta right now? The entire royal family basically got wiped out. So, if Imu wanted to take control of Alabasta, NOW would be the time to do it. So, the next Knight of God might just be a figurehead that Imu puts in control of Alabasta as a stooge for the World Government. But, who? Well, if Imu could corrupt or resurrect Cobra somehow, that'd actually be a pretty big reveal. King Cobra getting "reset" to his prime, and eventually having to fight his daughter. But, failing Zombie-Cobra, I feel like someone from the former Baroque Works would make the most thematic sense. The problem is, most of those guys are either redeemed, or working with Cross Guild right now. So...umm...I guess I'm going with Miss Father's Day, the frog-girl? She's the only one with a memorable enough design left. Not very hype, but it would make sense from a world politics perspective.
Another option would be someone from Amazon Lily betraying all their sisters and joining the God's Knights, so that Imu could rule over their island. But, I just don't see any of these girls doing that to each other. I don't remember there being any particularly "shady" or "ambitious" Amazons. So, it'd be too much of a swerve, I feel, to introduce one now. The same basic idea goes for the Revolutionaries and the Charlotte Family. I feel like they're too loyal to each other to betray each other...probably.
So, out of everyone, I think the most interesting options would either be Saint Shalria, Arlong, or someone from Alabasta put in place as the new World Government approved ruler. I think those are the options that would both make the most sense, and be interesting enough reveals to keep the audience invested. But, again...most likely Oda will just create someone new. We haven't even met all the present-day God's Knights yet, if there are around 8 of them. So, plenty of chances for Oda to make up new designs.
