Its worth considering the UAs that haven't made final products yet (so ignoring the Artificer/Eberron and Forgotten Realms ones)
Horror came out May 2025. We can assume most of that UA will go into Ravenloft (June 16th, 2026)
Psion also came out in May 2025 and revised in October. The Apocalypse Subclasses came out in August.
Arcana came out in June 2025 and revised in September. Arcana Unleashed releases Sept 16, 2026.
The "Mystic" subclasses only came out in January. I wager they aren't for Arcana Unleashed (the Mystic vs Arcana naming of the UA is big hint, but I could very well be wrong).
The Subclass Revisions Came out in October. It was a hodgepodge of revised martial themed subs, and it was the last one of 2025.
So this is my guesses.
The Horror Subclasses are clearly for Ravenloft, with the possible exception of Hexblade (which might go Arcana Unleashed instead).
The Arcane Subclasses are for Arcana Unleashed, again with Hexblade being a wild-card between products.
The Revised Subclasses COULD be for the Champion book, but there isn't a lot of meat here yet. Two barbarians, a fighter, a monk, and a paladin sub. And we don't have stuff like spells to pad the book out with, plus ALL of these are retreads, nothing new. I don't think we're getting a martial book in Champions, or if we do, its gonna be very lackluster. That said, I don't have a clue where these go save for a general book of revised options...
The Mystic Subclasses are too new. UA seems to generally go a year from initial offering to final product. I don't expect these until 2027. I suspect there will be a Mystic Season sometime next year.
The Psion and Apocalypse Subclasses All fit the window of UA release perfectly (Psion will be almost two years from the first IA, Apocalypse a year and change).
Other Considerations:
I don't think the Psion is appearing anywhere but the Dark Sun book first. It playtested with the Wild Talent feats and those appear to be the special category feats (dragonmark, dark gift) of Dark Sun. Though Abi-Dazim's Horrid Wilting was in the Psion UAs and appeared in the preview for Arcana Unleashed. Take that all as you will.
That said, if a new official class was coming in Arcana Unleashed, they'd have screamed it from the rooftops as a selling point.
If Dragonlance was going to be redone, I think the Lunar Sorcery (DL's only unique subclass) would have gotten a revision playtest. And nothing that has been playtested screams Dragonlance.
I'm assuming nothing that didn't get a revision UA (Arcana and Psion) got so red-marked that they are abandoning it. Of course, that could absolutely throw things into chaos, but my guess is even if something redlined, they would just replace it in house rather than abandon the whole idea (See Purple Dragon Knight/Banneret).
COULD anything happen? Sure. But I'd put safe money on Dark Sun this December (and the reason they didn't announce it is they want a big fanfare for it all on its own).