And it will be free! The latest post from Mike Mearls on the Wizards site explains this important piece of the new 5E D&D:
"Basic D&D is a PDF that covers the core of the game. It’s the equivalent of the old D&D Rules Cyclopedia,
though it doesn’t have quite the same scope (for example, it won’t go
into detail on a setting). It runs from levels 1 to 20 and covers the
cleric, fighter, rogue, and wizard, presenting what we view as the
essential subclass for each. It also provides the dwarf, elf, halfling,
and human as race options."
The same core classes and races as the original Basic set in 1977. Perhaps even a bit closer to Holmes than later Basic sets, since presumably it won't have race = class, thus giving demi-human thieves among the options.
"But the best part? Basic D&D is a free PDF. Anyone can
download it from our website. We want to put D&D in as many hands as
possible, and a free, digital file is the best way to do that."
"If Basic D&D is the equivalent of the classic Rules Cyclopedia, then the three core rulebooks are analogous to Advanced Dungeons & Dragons. Want more character options? Pick up a Player’s Handbook. Looking for more critters for your campaign? The Monster Manual has you covered. Want to sculpt a unique campaign? Pick up the Dungeon Master’s Guide. Still, Basic D&D is the true heart of the game and could easily provide a lifetime of gaming."
"At the launch of the D&D Starter Set, Basic D&D will include the material needed to create characters and advance to 20th level. In August, with the release of the Player’s Handbook, Basic D&D
will expand to include the essential monsters, magic items, and DM
rules needed to run the game, along with the rules for wilderness,
dungeon, and urban adventuring. (The Starter Set already covers the aspects of these rules that you need to run the included campaign.)"
20 levels is way more than I expected. That's all of B/X plus more. Way back in OD&D, Gygax wrote, "There is no theoretical limit to how high a character may progress, 20th level Lord, 20th level Wizard, etc."
"As we introduce new storylines like Tyranny of Dragons, we’ll also make available free PDFs that provide all the rules and stats missing from Basic D&D needed to run the adventures tied into the story. The adventures released as part of Tyranny of Dragons are playable without requiring any of the core rulebooks or the Starter Set. With just the Basic Dungeons & Dragons rules, you can play D&D for years."
"Basic D&D makes it easier than ever for new players and
DMs to jump into tabletop RPG play. We’re involved in the greatest
gaming hobby ever invented. It’s time to bring that hobby to everyone
who wants to take part."
In view of this, I'm still inclined to think of the new Starter Set as a "module plus". The original versions of B1 and B2 had a number of
pages of DM guidance for Holmes Basic. Plus B1 had a bunch of pre-gen
characters. The new Starter Set sounds like an expanded version of this. The free pdf is the Basic rulebook, the Starter Set is the module for DMs.