Essentials marked a violent change of direction for 4e, really, Essentials presaged some of what 5e aimed for: natural language, aesthetics like the Red Box, 'Player's Option' & 'Survival Guide' titles meant appeal to returning fans, a flood of errata 'to bring into line with the classic game' (followed by a near-moratorium on errata to actually fix balance issues), daily-less 'L' fighters & 'Thieves,' spell-accumulating 'Q' wizards, and casting rangers, in a doomed attempt to appease edition-war critics, etc... all too late (at only 2 years in), and too little (because of trying to maintain compatibility to 4e).
That included a planned Class Compendium that re-jiggered the PH classes to fit the Essentials aesthetic, which may be what you're thinking of, but it was scrapped as too-blatantly selling the same material twice (something Essentials was already doing pretty aggressively), and the modded classes-as-sub-classes released on-line (I think DDI, but could've been free).
Prior to Essentials the direction 4e seemed to be to putting out additional PH, MM, & DMG products almost annually.
- A DMG III could thus have been expected, and it would have been consistent with the DMGII's focus on Paragon levels if it had focused on Epic.
- An even-later PH IV might presumably have added a full slate of 4 Elemental or Shadow source classes (presumably Shadow, since HoS preceded HotEC), like PHIII added 4 psionic classes and PHII 4 primal classes (the 'no gridfilling' assertion notwithstanding, they filled every grid but Martial). Also, judging on the Psionics trend, you might well have seen new advancement structures beyond AEDU, though still balanced with AEDU through resource parity, like Psionics (which substituted short-rest-recharge Power Points for Encounter Powers).
- There'd likely have been a Shadow Power & an Elemental Power before Arcane/divine/psionic/primal got Power II's - and all that and perhaps more before seeing a Martial Power III.
- 4e MMs did not follow themes, particularly, so a MMIV wouldn't likely have been anything like Threats to Nentir Vale nor the MV.
- They also seemed to be working their way through the world axis, there were books for the Astral Sea & Elemental Chaos, already, we could probably have expected, similar 'secrets of' books for the Shadowfell and Feywild, expanding on material in the Manual of the Planes, and probably including what non-player-facing material was in HoS and HotFw.
- 4e was also working its way through settings, we'd already seen FR, DarkSun, & Eberron - I can't recall any indication what classic setting might've been next, but probably not the development of "Nentir Vale" we saw with Essentials, the original direction was for the 'default' PoL generic setting to remain generic.
- Finally, The VTT was sorta working by the end, so presumably, development might've continued on that and, maybe, even finally completing the promised DDI tools, putting the CB on an app, etc.