It's fun reading people's speculations...
...and here's mine:
Wizards still has time to tinker and if there are 8 PC races I think they'll be:
1) Human
2) Eladrin
3) Elf
4) Dwarf
5) Halfling
6) Half-Elf
7) Tiefling
8) Dragonkin (a toned down version of Half-Dragon.) Remember that playing a dragon or some kind of draconic character has been a popular wish - even back in 2nd Ed we had a whole setting product called Council of Wyrms that caused a buzz for a while. In 3rd Ed all kinds of draconic character themes sprouted (Races of the Dragon & Dragon Magic), so I would not be surprised if the 8th race is a draconic in some form. If so, it could still be a bruiser with the right class options, or a powerful caster in the hands of a clever player.
What I wish Wizards would consider:
Expand the roster of player character races with a few more choices and add the stats for some sub-races.
1) Humans (add suggestions for culturally-based modifiers to skills as an option to assist in enhancing character diversity, especially for human-dominated campaigns)
2) Tieflings (and provide the stats for their celestial counterpart whatever they may call it)
3) Elves (I really do not like the Eladrin concept, just offer High, Grey and Wood sub-types. 3 variants. Nice and simple)
4) Dwarves (providing choice of Hill, Mountain or Duergar toned-down)
5) Halfling (providing choice of Lightfoot, Tallfellow, and Deep)
6) Minotaur (Krynnish-like)
7) Lizardfolk OR Dragonkin (one scalykind race as a core PC is just enough IMO)
8) Kenku (flight available with character advancement)
9) Thri-kreen
Having a few "exotic" fur/feather/scale/bug types steers the D&D game further away from the LotR paradigm without dumping it altogther. A slightly larger choice covering a broad range should appeal to many and it would be easy for groups to trim back the choices at the gaming table if they so choose.
Just my thoughts
PS: I am concerned that a slavish devotion to market research statistics, a practice that is rife with risk and corporate delusions of granduer, will undermine brave and clever ideas. Just because Elves are "popular", do we really need both Eladrin and Elves and Half-Elves? Ugh!

Isn't a more even spectrum of races, peppered with some novel ideas, a smarter and more creative move? If one wants to be the market leader then one must actually lead and not cave-in into trends and fads fueled by the transitory success of the competition (Elves and their ilk in anime, Saturday morning cartoons, WoW, etc. Can we say overkill? I see it.). The folks at Wizards should separate themselves from the likes of Hasbro IMO, then they can actually be free to take D&D to new, non-elf-centric heights. We'll see by mid-December...