My gut reaction to the WoW Cataclysm rumors was to conclude that all races would be allowed to become all classes when the dust settled. I figured that there was no reason to keep any restrictions once you've explained away many of the most prominent discrepancies. Over the day since the leak, though, some of the examples I cited turn out not to be so far fetched. Is Blizzard opening all classes to all races, or have they just gone through and tried to stretch the rules using whatever exceptions they could find without (technically) breaking the lore (a fictional creation that they own and can change)?
Let's assume for the sake of argument that the 11 new combinations, and only those combinations, are going to be added to the game. Once the lore is accommodating those choices as NPC's, there's no reason to restrict player characters. What would that do to faction balance? Of the game's 10 classes:
3 are open to an equal number of races on each side. DK's and now Warriors will be universal (I'm pretty sure that BE's only lost warriors in the first place due to the pre-Wrath 6 classes/race restriction), and one race on each side (Draenai and Tauren) has previously been ruled too large to sneak in the shadows as a rogue.
After the changes, the Horde will hold a one-race advantage for Warlocks, Hunters, Druids, and Shamen. This could be remedied if the Worgen, but NOT the Goblins, get those classes. Gnomes would be the other no-Hunter race, and it might be argued that having such a large differential between character size and pet size (think Gnome/Goblin + Devilsaur) would be a PVP balance issue. Then again, would they really make Goblins go without hunters?
Meanwhile, the Horde would continue to have a one-race deficit in Priests, Pallies, and Mages. Orcs would be the only no-priest race, Tauren would the only no-mage race. However, there are issues with trying to balance this. Would they really rule out Worgen priests and mages? And is Azeroth really ready for Goblin Pallies?
Even if you conclude that Pallies and Shamen can remain imbalanced for historical reasons, that leaves Worgen with six classes (War, Rog, DK, Lock, Hunter, Druid) and Goblins with only five (War, Rogue, DK, Mage, Priest). More likely, there'd be some overlap (currently the Alliance has an extra warrior and priest, while the horde has extra locks and hunters), because I can't imagine new races in an alt-friendly expansion being limited to a mere 5-6 options (putting them in at least a tie for fewest options in the game).
One strange addition
So it turns out that, while the Bronzebeard Dwarves of Ironforge (all current player Dwarves) don't do Shamanism or Arcane magic, Wildhammer and Dark Iron Dwarves do. I'd also forgotten that the mages in Dire Maul were Highbourne pre-Night Elves rather than High/Blood Elves. Some of the others (Human Hunters, BE Warriors) were only left off because of the old class cap.
Still, what's up with Troll Druids? I don't recall ever seeing any druids beyond the two current races (Tauren and Night Elf). I suppose that the trolls (bosses in ZG, ZA, and ZD) have some ability to change into animal forms under the proper circumstances, so perhaps some off-shoot tribe actually learned how to druid without going nuts and sacrificing their totem gods. Worgen, whose lore is almost as clean of a slate as the Draenai, could also sneak in under the shapeshifting clause.
After the changes, six classes will be nigh ubiquitous, with the remainder (Warlocks, Druids, Shamen, and Pallies) being the classes that would be most impacted by racial culture if restrictions are remaining. As I noted above, there are three classes that will be missing from only one of the current races: Orc Priests, Tauren Mages, and Gnome Hunters. Perhaps arcane power is not really a Tauren thing (though I would have been Horde all the way if Tauren mage had been an option back in 2004), and Gnomes don't care enough about nature to feed a non-demonic pet. But why the hate for Orc Priests?
Speaking of Gnomes, the addition of priests would rescue them from their current status as the only race that cannot heal. This ends five years of oppression, during which Gnomes were the only race that could not organize a single-race dungeon run. Even so, they would still be the least versatile race in the game, with only six class options. (The other race with similar current limitations, the Tauren, picks up two classes at once to jump out of the tie for last place.)
Forsaken Blood Knights are another seeming omission. If you were going to add just one Pally race to the Horde, Forsaken learning to leech off of the baby Mu'ru from their Blood Elf colleagues seems more likely that Tauren spontaneously developing Naa'ru worship like Alliance Pallies.
Overall, my gut reaction to the changes may be been premature. Every non-gnome race would now be missing 2-3 classes (/mourn gnomes who miss out on 4), and most of the omissions make some amount of sense. The Druid thing remains dicey, but I guess that having at least two choices per class per faction is a worthwhile goal. And hey, I've been meaning to try a Shaman, but not all that enthusiastic about A) the Space Goats or B) rolling Horde without access to all my heirlooms and alts, so perhaps I'm just the audience they're after.