OK so 989 has changed pretty much all of the Straw Hat related matchups. The plan currently seems to be that Luffy heads up for Kaido, accompanied by Zoro, and the rest of the crew deal with the battle on the ground. This leads me to a pretty interesitng (albeit very controversial) theory about potential endgame matchups, should 989 be where the road to final battles begins.
Here's a set of matchups I think we could see:
Luffy vs. Kaido
Kidd & Law (and maybe Hawkins & Drake) vs. Big Mom
Zoro vs. Jack (!!!)
Jinbe vs. Queen
Sanji vs. King
Now, one of these might stand out as controversial, especially to a certain demographic. But hear me out:
Luffy and Zoro are the two Straw Hats said to be heading to the top. Zoro wants a piece of Kaido, but I don't think he'll get that chance immediately. Sure, you can say "oh but Zoro says he wants to fight Kaido so he will", but Zoro also said that about Doflamingo, only to have to deal with Pica. I imagine once they finally get to the top, the Scabbards and Minks will mostly be a spent force (I wouldn't be surprised if all the Scabbards were dead or dying by the time Luffy makes it up). That leaves one mammoth-sized obstacle in the way of Luffy vs. Kaido - one that Zoro will deal with.
I can hear cries of "Oh but Jack is the weakest of the All Stars he's not good enough for Zoro", to which I have to say this. Unlike the Big Mom Pirates, where Katakuri was said to be the strongest Commander pretty much from the get go, there's no such distinction with the All Stars - so as far as big takedowns go I'd say they're pretty equal. Also, we've already seen that Jack's a pretty monstrous fighter - he fought non-stop for days on end on Zou, and he survived an attack from Zunisha pretty comfortably. Combined with his Devil Fruit, it suggests he's incredibly physically robust - perhaps even more so than King or Queen. I'd even go so far as to argue that he's the most difficult All Star to take down in terms of "hardest one to cut through". That, and Jack is the most "established" within the story - there's pre-existing beef with him. I think that's a really satisfying takedown for Zoro that's far above the level of opponent he's faced so far.
Jinbe vs. Queen is an interesting matchup purely based on their personal roles within their respective crews. Whilst Jinbe is the new recruit, he's already worked with the Straw Hats before and he gets a lot of respect from them. That, and the fact he's a former pirate captain highlight his natural leadership qualities. Of the three All Stars, Queen is the one who's seen to be rallying the troops at the start of the Fire Festival, and we see him leading subordinates more often than Jack and King, the latter of whom seems to be more of a lone wolf. Jinbe vs. Queen is a battle of "leaders", and I wouldn't be surprised if that's the battle that affects the momentum of the war.
Sanji vs. King was briefly shown in 988, and when I saw that matchup the only thing I could think was "how did I not think of that before". As far as type matchup goes, they're perfect - Sanji is the only Straw Hat besides Luffy that can match King mobility-wise, and King's "Wildfire" epithet seems like a perfect rival for Sanji's Diable Jambe. Which flame burns hotter, I wonder?
As for the Big Mom matchup, I think for now that's going to be the jurisdiction of Kidd & Law. They're both still on the ground, and I imagine Luffy barely manages to get away, leaving an angry Yonko on the ground. It'd be the perfect time for those two to show their credentials as Luffy's main rivals. The reason I have Hawkins & Drake as potential inclusions for that matchup comes from them possibly betraying Kaido if they sense they have a chance to take down a Yonko. We already know Drake is a double agent with the Marines, so he's not exactly loyal, and we know Hawkins was originally allied with Kidd. I'm not 100% set on that idea, though.
Another series of matchups I'd really love to see is the remaining Straw Hats against the Flying Six (minus Drake):
Usopp & Nami vs. Ulti & Page One - I originally said Sanji & Nami, but now we've seen how the war is going I think this could be a really cool matchip. Page One & Ulti are somewhat of a dysfunctional duo, and I think Nami & Usopp could pull off an upset by being the better team.
Chopper & Robin vs. Black Maria - Black Maria kinda big. You know who else is kinda big? Monster Chopper. I think Chopper and Robin would make for a really interesting combination against her, since they both have abilities that would help overcome the size difference.
Franky/Brook vs. Who's Who/Sasaki: I think this comes out as 2 1v1s, but I can't decide which way around they'd go. Both seem like interesting opponents for Franky - Sasaki has that kinda robust, manly look about him that makes him look like he could take part in another suplex matchup, and Who's Who has his crew with the girls in cat uniforms in that remind me of the Franky Family girls (Mozu & Kiwi?) and Senor Pink's fangirl army. Both carry swords as well, so they could be equally fun matchups for Brook. Franky and Brook both seem to be in the mood to take out someone big, and these two would certainly be huge scalps for them.
I'm not sure what Yamato does (maybe one of Orochi/Kanjuro resurfaces and he deals with them?) and I'm not 100% set on Marco (he might end up having to deal with Perospero or other Big Mom crew members), but overall I feel like "Straw Hats vs. Beast Pirates" is the key battle going into this, so I think the final matchups should reflect that.