I think the first PHB should only deal with the common races of the presumed setting. Unless tieflings, warforged, etc are so common as to have entire counties composed only of such beings they should not be in the PHB #1. PHB #2 sounds like a good spot for such races: fringe and uncommon beings that perhaps are well enough known that no one stares in shock / horror / awe / incomprehension upon seeing them.
PHB #1 should have humans, elves, dwarves, and perhaps one or two other races in it. If half-orcs become the new 'orcs' - having entire tribes, hordes, etc composed of such - then they too should be in the PHB #1. From what I've heard it seems that gnomes may not be in the PHB #1, but if that is the case then Halflings definitely should be, as half-sized races seem almost as common a fantasy archtype these days as orcs or elves or dwarves.
So, I would expect in the PHB #1 the following races: Humans, Elves, Dwarves, Halflings, and (half) Orcs. I might be able to see Hobgoblins as a race in PHB #1 also. I would prefer no half races, and if half-orcs are included I will treat them as orcs and ignore any fluff that suggests otherwise (and the crunch of 'full' orcs, perhaps using them as a monster of another name).
And in PHB #2 I would expect: Gnomes (as they are not in PHB #1), Warfoged, Tieflings, Aasimar (or Eladrin, or whatever the good equivalent of the playable Tiefling race will be), Changlings, and perhaps Shifters &/or Genasi. Goblins might also work well as a race in PHB #2. With the exception of Gnomes (and possibly Goblins), these are odd, fringe races, often portrayed as low in number, diffused throughout populations largely of other (major) races or shunted into sparsely populated frontier / wilderness lands, and often looked upon oddly if not harshly by other races.
PHB #3 would / should be the first to start putting in the odd / new races for 4e, as the common and uncommon races have already been covered in PHBs #1 and #2. It probably will not work out this way. I expect to see fringe races mixed in with common races in the first PHB and arguably even with the second one.
I am beginning to wonder about some things. I recall when 3e came out some of the comments made about orcs when some of the books began focusing on odd combinations such as orc paladins and such. Over time it was viewed as less and less odd to see such strange combinations of class and race. I wonder if the Tieflings will take this role in 4e - such that we will start seeing Tiefling Paladins as suggested example characters in later suppliments and so forth. I hope not, but I would no longer be surprised.