100% not set in stone but I think the signs point to Worgen and Goblins as playable races. At least in my opinion;
Worgen = Alliance
Goblin = Horde
It seems possible that the new faction change thing would lend you to think that they might start out 100% neutral with a quest line to ally your with your faction of choice, but I just don't see how that'll work with AH and mail and PvP.
I mean would you ONLY have access to old world type goblin AHs (Gadget, etc...) till you took a side?
What about BoA items with the +10% XP? As of now you CAN'T send BoA items gained on say a Human Rogue to a Tauren Druid on the same server PvE, PvP or otherwise. What if you have that same Human Rogue and send your neutral Worgen Warrior BoA shoulders and then you choose to go Horde with the Worgen, then send the shoulders to the Tauren Druid. Did you just circumvent the system? Then again maybe the whole faction change thing changes make this last paragraph a moot point.
In terms of PvP, I don't know about you guys and gals but having both races on both faction in a scrum in a BG would be annoying. Of course the Red or Green text would give it away as which faction they are, but it would just seem... sloppy, I guess the word would be.
What about guilds? Your in a Horde guild and the expansion hits. You want to retire you Troll Warrior and play a Goblin Warrior. You create the Goblin and can't join your guild for 10-20 levels, till you pick the Horde faction? Can you even talk to you guildmates? Can you talk to both factions? Neither?