I'm going with mid-to-late 2026.
Honestly? I'm expecting some sort of a "eject button" plot device to come into play to get Imu out of here. I doubt we'll get a full Imu fight right here and now. Oda's probably saving any "main" Imu fight for later. So, Imu can't use their full power here and now. And if Imu falls or retreats, I'm expecting Sommers and Killingham to retreat, too.
Plus, remember, Gunko is actually the only God's Knight who's here "physically". Gunko and Shamrock are the only ones who came through the Abyss Mark in the Throneroom. Sommers and Killingham were summoned by Gunko, and Imu's only possessing Gunko with some sort of power. So, if that works similarly to how the Gorosei seemed to work back on Egghead, that means the other God's Knights can be blasted away by Haki. Just like how Joyboy's Haki Knot removed all the other "summoned" Gorosei from Egghead, but left Saturn behind, since he was the only one who was there "physically" instead of being summoned.
So, if there's another Haki Knot somewhere on Elbaph, then everyone except Gunko would probably get blown away by the blast.
Or maybe Franky presses a button in that 3000 year old lab he's exploring and forms a "Haki Force Field" around the island, which does the same thing. Removing Imu by force....field.
Or maybe Luffy just freaks Imu out with his Nika form, and Imu's panic attack causes everyone to retreat by reflex.
Or maybe Luffy and Loki teaming up creates a attack that's SO overwhelming it just blows Imu away. Garp/Roger team-up style.
Or maybe things get so bad back at Mariejois that Imu has no choice but to order a retreat, because they just need the backup that badly.
Or maybe even Brook can do something to disrupt Imu possessing Gunko with his Soul Powers.
Or maybe Blackbeard makes his move on Imu's "physical" body back at Mariejois, and eliminates the possession that way by coincidence?
There's several different ways this fight could end early. And I'm expecting Oda to pick one of those options. I think Luffy and Imu will at least SEE each other during this arc, but I'm not as sure if that will lead to a actual fight. After all this buildup, that might be a little disappointing. But, personally, I think Oda's kind of done with this arc and wants to move on. So, chances are, we're going to be ending the fight a little early.
Now, the real x-factor here is everything else. Because, it depends on how much other stuff Oda wants to do after the fight. Because, it seems like Scopper has something else he either wants to tell or teach the Strawhats. Just so they have a chance to get a little power-up. I don't think we'll be doing a full training arc. But, we might get a montage while we pop around the world, or something.
And I feel like Oda really should show us what's going on with Mariejois at some point. So, I could see us getting a few chapters there.
And then there's the whole Heaven/Astral Realm to see, which isn't mandatory, but would be nice.
And then we could use a update on what's going on with Vivi and Big News Morgans. Or Law. Or Bartolomeo. Or Blackbeard. There's a lot of "intermission arcs" we could get.
So, I think the Elbaph fights will almost definitely end by this year. Maybe even the middle of this year? But, depending on how long the Elbaph epilogue and "intermission arcs" are, we may only JUST get off the island by the end of the year.