Personally, I think this goes out the window as soon as you make changes to the basic class structure. If they'd released a new class under a different name, or released a "PHB 2" with an reworked set of subclasses, I'd buy that as the level of change. But they're selling core books again, and they're saying the Fighter works differently now, and there's a conversion guide for older fighter material, which slides this solidly into the 3e->3.5 camp, instead of the 4e+essential situation. It's non-errata replacement changes, instead of "additional material that's also a viable starting point."
Essentials remains a really interesting point in D&D publishing history. The content had an audience problem (the 4e core fans hated it, the target audience hated 4e too much to look at it) which meant the underlying strategy, "here's some slim books that you can use instead of the core books to play D&D, and it's a little different/simpler" didn't really get a fair shake. We're not talking about groups that bought the Monster Vault, Heroes of the Fallen Lands, and threw together a campaign now, we're talking about how essentials and core PHB classes played at the same table.
I think the 5e version of that is probably something like releasing a small book that has a new "Warrior, Thief, Magic-User" base classes, that are almost, but not quite, like fighters/rogues/wizards. Probably with rules that let you use wizard spells as an MU and vice-versa, maybe with subclass parity across the two, or a conversion process that's like "you can add this generic ability at X level to every rogue subclass to make it a thief subclass" or "this level 2 warrior feature can be replaced with the first subclass ability of a fighter if you take a fighter subclass on a warrior." Then you take some late stage 5e optional rules and present them in that booklet as normative, casually rename race to species with a sidebar saying it's the same thing and so on.
Honestly, I could see an interesting publishing model for D&D where you have multiple "expandalone" style books that could all function as a core set of classes, and could be enough for a group to play from.