I would throw in orcs as well; they may not have been a race as long as the ones you've mentioned, but they've been a core part of D&D at least as long. Then I'd put out a race book - call it "Beings of Myth and Legend" or something - and that's where I'd lay out races like dragonborn, the planar races, etc.
I'd do it like that for two reasons. First, while I'm not on board with Yaarel's idea of a bare bones stripped down core book, I do think that a "classic D&D" approach to the core is a good idea. The difference is that I think that the core should be less bare bones, and more like a good soup stock: flavorful, but not too exotic. It shouldn't just be "hey, here are the rules of D&D," but "hey, this is D&D." Now, arguably dragonborn at least, and possibly tieflings as well have become part of what younger players consider the core of the D&D races, but that brings me to my second reason.
Races like dragonborn, and definitely the planar races are varied enough in possible origin and configuration that I feel they really need more room than the PHB can afford to do them justice. If I had my way, there would be a revisiting of the "Complete" series concept from 2E, giving every major race their own book filled with potential lore, adventure ideas and player options. Alas, it's not an idea that would sell well enough for today's WotC. But I still think that at least having a race specific book could give enough real estate in the book for the more exotic races to get the kind of options and imagination fuel they need. I'd give multiple potential origins for groups to consider, each with at least as much text as the race would get as a whole if it were in the PHB. I'd take the barebones approach the playtest is suggesting will be the status quo and give multiple advancement paths for players that want their character's race to play a bigger role mechanically. In the case of races with varying potential appearances like the planetouched, I'd dedicate a page to ideas for players to use to imagine how their character would look, potentially with tables for those that want a little help in that department.
Basically, I'd give let the PHB be D&D comfort food, and then put out a recipe book for those that want more.