Regarding Triton, while I would love for him to have a story with the Keyblade, he's also a demigod king of the Seas with an all mighty weapon who seems to be at least on the same powerlevel as a Keyblade.
Triton also knew the shell in Ariel's grotto was the Keyhole for Atlantica and Keyholes weren't even a piece of plot before KH1, so I doubt they would make a big deal out of him.
I have to disagree with you, just because he is a demigod and the rule of the seas means he's knowledgeable about everything including the Keyblade, besides he's not in the level as you say the Cheshire Cat, Magic Mirror and especially Merlin and Yen Sid.
To this day, King Triton's knowledge of the Keyblade still felt "forced" regardless of it, even after the release of the first KH game, which baffles why the Development team didn't even bother putting Atlantica in
Birth by Sleep and/or
X/Union X. :/
Besides the VAST majority of the Disney worlds and inhabitants (with some exceptions) don't know about the existence of other worlds, the Keyblade and the Keyblade War, which Atlantica and Triton do fall under.
I really want to have have Atlantica included in
Dark Road, so it would provide better explanation on King Triton grievance and hatred on the Keyblade which in his words "brought chaos and ruin". Besides, Atlantica hasn't appeared in ANY KH game since KH2 and it would be a missed opportunity to not include it in Dark Road.
I've seen others mentioning Wreck it Ralph being wasted as a main world in UX but (and correct me if I'm wrong because I only really watch the relevant story updates and not the Disney fillers) that world is only a data version over there like all others, meaning at some point someone carrying the No Name Keyblade had to go there to observe the real deal so it could appear in the Book of Prophecies in the first place.
So no, Wreck It Ralph isn't ruled out of reappearing in KH3 or in this game (What Keyblade would Xehanort even wield in the first place? I guess we'll finally see his and Eraqus original blades before they inherited No Name and Master's Keeper).
To be fair, I actually wanted a Wreck-It Ralph world ever since
Kingdom Hearts III entered development as the film came out around the same time that KH3 began production. Honestly, I wouldn't be surprised if the film was actually considered as world during the development of KH3 and was included as one of those worlds, but was scrapped very late in production when they heard that Disney was doing a sequel to
Wreck-It Ralph (
Ralph Breaks the Internet), which is why he ended up as a link summon in the final game, even Nomura confirmed it as well in an
Edge Magazine article
It's unfortunate as it would've been a spiritual successor to the
Tron worlds in past KH games and have it be a world-within Twilight Town either at the Old Mansion or some Taito Arcade building. Also in my unpopular opinion, I feel Dark Riku felt more suited as the seeker of Darkness for
Wreck-It Ralph than Big Hero 6 especially his mentioning of "Heart out of Data" which I'm going to be honest I don't even recall the original Big Hero 6 film talk about "Data" when compared to the Tron films (original and Legacy) and
Wreck-It Ralph which seems to have more mentioning emphasis of Data than Big Hero 6.
It makes me more curious about the Wreck-It Ralph world following it's story's conclusion in Union X
and whether we explore the events of the film for the next KH game. It could be another Space Paranoids/The Grid situation where Game Central Station (including Niceland, Hero's Duty, Sugar Rush) could've been copied and is a place explored by Sora or anyone for the next KH game.
As for world suggestions, I have some ideas:
- A version of Deep Space from Lilo & Stitch. Agent Cobra used to be from the FBI and he met the Gallactic Federation before the events of the movie and he knows how their rules work, being even used to them being a bit unfair sometimes. Xehanort could have a run with the aliens and dislike how the government hides confidential info from others for their own reasons, and it could also hint Lilo & Stitch showing up in KH4. Also, the Aliens seem to be older than the humans so young Gamtu could happen.
- Beast's Castle: Although I haven't seen the original movie to know if it was ever stated wheter the Beast and his servants still aged normally and the time limit was only imposed on the curse being permanent or not, I think witnessing the Sorceress who had to deal with the Prince's arrogant personality and seeing him becoming cursed in the first place is the perfect opportunity to showcase how humans can act when they have power over others.
- Emperor's New Groove: Izma is old. At some point she wasn't. I don't care, I just wanna see this world being used and I doubt it'll make into KH4.
- Atlantis and Treasure Planet: Both are fantastic movies who deal with humanity's greed at its worse and it's so unlikely for them to be featured in the main series that they might as well use them for this.
- Live Action Wonderland: The whole place is so chaotic and we are starting to deal with worldlines and parallel worlds, so Xehanort visiting an even more twisted version of Wonderland and being horrified by the Red Queen's actions could work. Plus, this time they could actually touch on the sequel.
- Prankster's Paradise: Gepetto is old, probably around Xehanort's age. Show us him in his youth as an incredible inventor and maybe reveal that his experience with building puppets goes further what we first assumed. The Blue Fairy had some relevance in the Limit Cut from re:mind too, so maybe retcon this with her having a story against the forces of Darkness?
- Dumbo: I don't want this world in KH4, and the whole Circus deal is perfect for the morale of this game. Plus, by being in a mobile game they have it easier to feature this story in a pocket format while avoiding going too realistic and dealing with all the racism.
I really envision Atlantis, Treasure Planet, the Live-action Wonderland and maybe Dumbo could work as worlds for the next KH game (bridge game to KH4) than Dark Road. Lilo & Stitch looks to be ideal for Dark Road and I agree that the world should appear in Kingdom Hearts IV, it would be a missed opportunity if it wasn't in KH4, plus his connections with Terra, Ventus and Aqua whom Stitch (Experiment 626) encountered during BBS. Honestly I'd actually would have Lilo & Stitch for KH4 over Moana. lol
Also when did the Blue Fairy had relevance in the ReMind Limit Cut episode? I didn't see her nor was she mentioned, it was the Fairy Godmother from
Cinderella who appeared.