I anticipate we'll either get a streamlined Character Rules Expansion book that combines some options like Death and Grave Domain or Undying and Undead Patrons, some options will be left out entirely, but most Rules Expansion options (and the missing Core Rules subclasses for Cleric and Wizard, but not Oathbreaker Paladin) will be carried over. I imagine some options like Hexblade will be more or less invalidated by core class features (I imagine Pact of the Blade will be a bit more robust in the finished PHB 5.2), but and they'll want to limit overlapping archetypes within the same class (ex. Banneret and Cavalier and Samurai for example all represent Knightly Warlords/Marshals archetypes within the Fighter and may be represented better with the expanded Battle Master options).
Alternatively, they slow drip them out so that they have time to UA the revisions to these other options and not just serve them up as is. Some options are probably near perfect (Swashbuckler Rogue, I'm looking at you; probably only cut for the sake of giving another Psionic option in the core rules). Other options probably need a lot more work and refinement.
I imagine to see updates to subclasses akin to the changes between 3.0e books like "Spells & Silence" -> 3.5e Complete Arcane. Not that I think this is a new edition, mind you, just that WotC has an incentive to sell us the errata in as many different books as possible first before giving us the compiled version. Especially now that you can't buy piecemeal options on D&D Beyond.