When I read this article, I see "fewer and fewer players were moving deeper into additional material such as the Player's Handbook, Dungeon Master's Guide, and Monster Manual", "early 1980s", "not just a sampler or a game that guides you through making a character and playing a single adventure" and "will easily find other products to migrate to if you so desire", and see Mearls saying they are going back to a D&D/AD&D split. Which is not to say they are going to create competing lines with different names. But it sounds to me like he's saying they are going to have a core game that is essentially like B/X (early 1980s!), and then "advanced" options in the Players Handbook, Dungeon Masters Guide, and Monster Manual. Players can go for the whole hawg of modules and optional systems, or they can stay with a simple, minimalist core game, and both will be supported with largely compatible adventures. The core game will be perfectly playable in and of itself, but will also act as a feeder system to the other products.
It's a model that worked pretty well for TSR back in the day.
What they are proposing isn't new at all, in fact, it never skipped an edition. If you wanted to keep it simple, you just used the core three and you were good. All editions were simplified, it was adding additional material that could make it complex. They don't really need to waste time creating a separate product that does this.