My two cents on the likelihood of hypothetical upcoming titles. Based on Nomura's previous statements, I think we'll probably get three of these:
KH4: Obviously 100% going to happen, but I wouldn't expect it to be released for several more years, with an official announcement only roughly 9 months before release. I'd anticipate Q4 2024-Q1 2025.
Spiritual DDD2: Almost definitely happening as the next title, starring Kairi and Riku in the RoS. I'm hoping for confirmation at TGS. With quarantines having certainly left everything in a state of arrested development, I wouldn't expect a release prior to Q4 2021 at this rate.
Spiritual BBS2: Eh, 50/50 chances. I'm quite sure that Nomura wants to do more with those characters, but I can't really envision much story to tell for a full-fledged 20-30 hour campaign, unless they somehow end up in the Age of Fairytales and flesh out that corner of the universe. A 5-8 hour long, 0.2 scenario of them in the RoD, encountering some new threat may be ideal.
Spiritual TWEWY 2/remake/crossover/Sora & Yozora's Shibuya adventure: Uh, something like that lol. Also 50% possible imo. I think you'd really need another Sora title before KH4 to explain his journey, post-ReMind, as well as Yozora's efforts to "save" him, separate from however Kairi and/or Riku may also try to. A great opportunity to flesh out a new worldline and secondary characters (TWEWY crew, Yozora, Luxord). We also need to learn about this robot enemies.
Union X console remake/CG movie: 40% likely lol. I think something of this vein is absolutely necessary, but I just don't see it happening. SE will be too worried about their dumb mobile game losing money.
Spiritual Days2: I think it'd be great to give RAXNS their own adventure separate from the main story, but I also think Nomura would struggle to keep them relevant outside of Axel and Saix searching for Subject X and perhaps seeking retribution from Ansem the Wise (which could instead be saved for KH4). I feel like Roxas, Xion, and Namine have all more than run their course at this point, though... Maybe another 0.2 minigame meant to give those characters a final sense of closure could work... So, like, 30% likely?
Pre-Sora Verum Rex prequel: Incredibly unlikely, and totally unnecessary. I can't imagine there being enough story and lore to warrant a full game exploring that world before Yozora becomes aware of Sora. There's no real reason to basically make an entirely new IP and then shove it into KH anyway.
An eventual console remake/CG movie of Dark Road: Nah, never gonna happen. If it ever was, we would've gotten that instead of another cash grab mobile game in the first place.
Any kind of title focusing on the likes of Xigbar/Luxu, Marluxia, Larxene, Luxord, Demyx, Ava, Mickey & Donald & Goofy, or Ansem the Wise: The chances are zilch. However, with the exception of MDG, I think there's tons of potential to work with any of these characters in a sub-game, and I also believe that it'd be the only way to do any of these characters true justice at this point. These characters are all just steeped in too much history and lore at this point to be able to continue to function as secondary characters in other titles that don't have the time to flesh out the backstories and b-plots of these characters. Like, as of present, there's a truly ridiculous amount of implications regarding AtW and his involvement with much of the series' mythologies, but none of the titles have the time to actually show these things. It's infuriating to me. I don't want to read about these things in optional reports! AtW could arguably be the series' most nuanced character, but you'd never know it because in-game cutscenes don't regard him as anything more than a combination of an expository device and a vehicle to mount suspense. Very similar sentiments could also be expressed regarding Xigbar/Luxu, whose varied history could never be condensed into a few cutscenes of droning exposition in, say, KH4. But alas, I can't see Nomura and SE recognizing the narrative and financial potential to routine sub-games released between main titles. 0.2 was a one-off of missed franchised potential.