Hmm... doing a bit of deductive reasoning here...
The 3.0 FRCS gave racial write-ups in the 'characters' section for a bunch of races in addition to the standard 3.0 PHB races. They were
- Gold Dwarves
- Duergar (LA +2)
- Drow (LA +2)
- Sun Elves
- Wild Elves
- Wood Elves
- Svinfneblin (LA +3)
- Ghostwise halflings
- Strongheart halflings
- Aasimar (LA +1)
- Genasi (Air, Earth, Fire, Water) (LA +1)
- Tieflings (LA +1)
Now, Races & Classes and various statesments from WotC people seem to pretty strongly indicate subraces are largely gone in 4e, and that they think all the varieties of elves out there can be covered by elves, eladrin, and drow. So scratch the elf, dwarf, and halfling variants. They've also said that they no longer think all races need a dark/underground/evil variant to go with the drow, which suggests duergar and svinfneblin will be pushed to the background if not eliminated.
Tieflings are already in 4e core. So that leaves Aasimar and Genasi as the leading candidates. Hints that they're doing more with elemental-themed stuff (like the fire archon article), and my opinoin that aasmiars (renamed or not) are probably more general than FR, suggests the genasi are the best bet.