I think it's obvious we'll see the Warriors and Mages, with full subclass representation. We'll finally have our answers for which 4 subclasses for each class they are most interested in showcasing in 2024. Unless a particular subclass gets rated very low, this will likely lock the subclasses in for the final book.
Because Warriors are front and center, I also think we could finally see any remaining updates to the weapon list and weapon mastery options. Do the designers agree with some players that Monks and Bards having access to only Simple Weapons is an issue? Or that short swords being Martial is an issue? Will they tweak Flex or other weapon masteries?
Because Warriors are front and center, I also think we could see a revisit to Feats, at least combat style feats. Perhaps feat prerequisites because Monks were originally pitched as "warriors" and because they are not proficient in martial weapons, they can't select many combat feats.
They may update and clarify the language for unarmed strikes/grapples/save DCs if they have feats that need to reference it.
The Mages will have their class-specific spells tweaked for flavor.
Sorcerer's Sorcery points and spells will be tweaked for balance and functionality. I'd be down for Sorcerers being able to use different ability scores for spellcasting, like the Warlock. I can see Wisdom for a Divine Soul. While thematically a Constitution sorcerer sounds fun, that would be too powerful if only because of the ability to be Single Ability Dependent compared to other sorcerers or casters.
Because the designers have said they want to try different variants for Warlock spellcasting, they may take one more stab at a different Warlock spell progresson/recharge variation before they abandon changes and go back to Short Rest recharges.
Wizards have really good ideas, but their Spell Modification and Creation rules need tweaked. They also need to clean up the language for Scribe spell so that it works right rather than suggest an illogic loop.