Let's think about what we know and try to extrapolate. Let's also add the caveat that when we did this two years ago, we thought we'd be discussing PHB4 right now.
1) Essentials is the core of the game. Just look at the flavor text in the themes articles if you don't believe it. I didn't see any mention of a single non-Essentials class in there. Any and all published framework-building will be on the Essentials chassis.
2) The idea of subclasses within classes seems to have caught on, and will continue. It's a good idea, and makes sense from a design perspective, because it allows use of pre-Essentials powers within post-Essentials design. After all, green is in, so recycle that 2008-2010 design work!
3) There are currently 10 Essential classes: Fighter, Rogue, Cleric, Wizard, Ranger, Druid, Warlock, Paladin, Assassin, Vampire. Of those, 4 have 2 essentials subclasses(ignoring the PHB1 repackaging oddities): Fighter, Ranger, Warlock, Paladin.
4) Although I don't think it will slavishly follow the HoS layout, I'd expect it will provide similar page count to races, classes, fluff, etc. So maybe one completely new class based on a previously released class, 1 or 2 new subclasses, a new class tackling a concept not previously released, and some more build options.
5) Conjecture here. New druid subclass based on the warden. New cleric subclass based on the shaman. It will still gets domains, but everything else is rearranged. Essentials bard. Fey-pact binder. Winter and Autumn Sentinels. I want to say swordmage or bladesinger like wizard subclass, but isn't that in Neverwinter? Essentials sorcerer will come out in Elemental Heroes.