Ideally, who would you like to see as the evolution trigger enemy for each of the Chosen? Feel free to make lists based on Ultimates, Dark Evolutions, or other evolutions you feel they might get.
WarGreymon-
I'd love to say Darkdramon. I think watching the two of them clash would be awesome. However, Darkdramon was already ShineGreymon's enemy in Savers. Titamon would be neat, but Ogremon kinda had a redemption already (and might be dead), plus he probably needs to evolve vs a -dramon. I do not want it to be against Mugendramon, and honestly I'd prefer to be done with Mugendramon for a long time. Breakdramon would also be cool. He's a giant -dramon with drills that could give WarGreymon's claws an actual run for their money. Plus, we've already seen Coredramon.
MetalGarurumon-
Slayerdramon would be an awesome choice since we've already seen the Blue Coredramon working for the enemy, but I'd only want this if Warg goes against Breakdramon (maybe at the same time?). Gundramon would be awesome too. Both have high mobility guns.
HeraclesKabuterimon-
It'll probably be GrandKuwagamon, but I really don't want that. EBEmon could be a nice reference to the original, and they could always use another bug like GrandisKuwagamon or TyrantKabuterimon.
Phoenixmon-
I really think Ornismon would be awesome. It had some great action in the Frontier movie, but I would love to see an aerial fight between these two giant bird Digimon. However, if the CannonBeemon was just one member of a larger Royal Base force, TigerVespamon would be my number one choice.
Vikemon-
Regalecusmon. GigaSeadramon.
Rosemon-
As ridiculous as it sounds, KingEtemon. Queen of Beauty vs the King of Kings. Seeing the two of them vs each other (false beauty vs true beauty) would be awesome and hopefully pretty funny too. Lotusmon boring, obvious.
Magnadramon/Ophanimon.
Regardless of which one they go with, I think Deathmon would be cool. He's a Demon Lord that isn't a part of the 7GDL. Also, we've already seen them in the series. I can see the potential "Final Ultimate" defeating it.
Seraphimon-
Murmukusmon would be a nice reference to Digimon Next. Demon Lord that isn't a part of the 7GDL. I can see him being attended by a Griffomon and working alongside Deathmon.
Omegamon *2nd Trigger.
He'll probably show up again against "Shademon's" Ultimate.
I would love for the last arc of the series to focus in on the Seven Demon Lords, and I thought about giving each Chosen a Demon Lord to evolve against, but I feel like they need to have their Ultimates by the time facing 7GDL becomes a thing. I tried to pick Ultimates that weren't a part of a specific group as well.
I'll edit this later when I have some more time to finish this up.