Essentials does have people worries about 'support' for pre-E stuff. It might make more sense to look at those worries by source, though.
If you look at HotFL, the material given for the Divine(Cleric) and Arcane(Wizard) builds is mostly useable by existing Clerics and Wizards. Like many builds, they have a few unique class features swapped around, and beyond that, their a little wierd in how they gain them. But, all the attack and utility powers of the Warpriest and Mage 'pass through' to the Cleric and Wizard. The same is not true of the Martial (Fighter and Rogue) builds in the books. Only the new utility powers - a relatively minor component of any class - 'pass through.' HotFK is similar, the martial builds recieve minimal pass-through support, the other sources a bit more (though not so much as the Wizard gets from the Mage).
In order to 'see support,' for the non-martial classes, all that needs to happen is a new build for the class needs to come out, and it's powers, at least, pass-through to the parent class, which is 'suppported.' For martial classes, though, new material will either be Essentials-style or 4e, and would support only the corresponding builds. HoS, so far, gives more pass-through support only to the Wizard, Cleric, and Warlock. The one hybrid-martial build is virtually stand-alone, possibly passing some tidbits to its parent class, the DDI-only Assassin. And there's one - one - Shadow class.
Now, in the past, if a _______ Power book came out, it would mostly do stuff for it's source. There wouldn't be a lot of goodies for Wizards in Martial Power or Rangers in Arcane Power. But, in HoS, there's only limitted goodies for the one pre-existing Shadow Class, a 2nd new Shadow Class, and support for Divine and Arcane classes (classic casters).
That's odd. It's also consistent with part of the 'new direction' being a return to the disparity between casters and non-casters that plagued prior editions of the game.