I like their current presentation choice of races in the latest playtest packets: the classic 4 being presented as Common, and the rest basically as examples of races that may or may not be available for PCs, largely dependent on the DM's choice of fantasy setting.
If they stick with this presentation for the final product, it makes races beyond the classic 4 more acceptable.
The problem though... is that the word "Core" is a loaded term. And people have been using it to whine to high heaven about what appears in the books and what they do and don't want to see and use for years now. Using the word "Core" serves no function other than to make some people demand that things they want should appear in the first set of books, or things they don't want should not.
Now yes, the first three books absolutely give us the first group of rules we will use to play the game. I have no problem with that. But by calling those rules "Core"... it makes anything that appears after them "not Core"... and thus people will use those definitions as a bludgeon to try and get their way.
Screw "Core". Rules are rules, regardless of which book they come from. Stuff from Book 1 is no more important than stuff from Book 3, and the sooner we start accepting that, the better off we'll all be. And maybe then we'll stop hearing the ridiculous complaints that the dragonborn don't belong in Book 1 for example. That race has just as much right to be in Book 1 as any other.
Where really "Core" has some meaning, is in how all the subsequent published books assume it is available at the gaming table.
In 3e, non-setting-specific supplements would directly reference core material only. It's a safe choice to assume that every gaming group owns at least the PHB, DMG and MM (there are only rare cases of groups where the DM decides not to buy the DMG for instance) and therefore all the material in ONE supplement can directly reference "core" material or build upon it.
In 4e, I remember that "everything is core" was often quoted, but I don't know what it meant in practice. When this is meant that every book can reference every other books (and not only the 3 core), then the whole can become a mess. There will be people buying a book and discovering that they cannot use part of its material unless they also buy another book and so on. This might still work fairly well within a specific campaign setting, at least if the number of books for that setting is not too large.
OTOH, cross-referencing material can be a good thing for the game, but obviously only if you own both books. IMO this should rather be made available online.