While this speculation is entertaining, lore is just one of the facets of adding new races to the game. I'm rather shaky on the worgen-Alliance connection; remembering the Scythe of Elune quest line, worgen are hardly fluffy cuddlebuddies, and it'd cause some rather odd lore moments for a level 27 Worgen Hunter to slay Nightbane Dark Runners for Calor in Duskwood. I just can't see how they'd reconcile that.

But from a world design standpoint, the REAL reason why the Draenei crash-landed on Azuremyst Isle is because it's right next to Teldrassil and Darkshore: existing low-level areas affiliated with the same faction; it works out very conveniently. The problem with Gilneas is that its sole landward entrance is to Silverpine Forest, which is Horde Territory -- no friendly quests, and, of course, you get flagged on a PvP server. Level 20 wolfcubs fresh from Gilneas can't be sent to Silverpine, not to mention the closest Alliance town is Southshore, and it only offers quests in the level 30+ range.

So with the assumption that Gilneas is the Worgen starting zone, Blizzard would have to either develop 30 levels of questing, compared to 20 in the Burning Crusade, or provide transportation to a zone that offers quests around level 20: Menethil is a bit of a stretch as the entire Wetlands is designed around the assumption that you'll enter from Loch Modan, and funneling people to Stormwind Harbor would be a copout.

One solution would be to implement a zone, for example, Kul Tiras, for questing for both Horde and Alliance (say, Goblins and Worgen) from 20 to 30, with links to the Goblin Capital, Ratchet, and Menethil. However, Blizzard has been historically reluctant to add content to mid-game (20-60) with the exception of the 2.3 revamp of Dustwallow Marsh. Effort-wise, it's easier to lower the mount requirements to level 20 and just let people level through the same content faster, that way they can add more content at the endgame.

Besides, one has to wonder what the benefits of adding two new playable races would be. Blizzard would have to develop at least four new zones, hundreds of new quests, design new quest rewards, all at a very low level. When the BC races were added, each of them contributed a new class to the possible offering of classes: Alliance players created Draenei Shamans, and Horde players rolled Blood Elf Paladins. Wrath added the Death Knight class, bringing the total number of classes to 10 -- same as the maximum number of characters on a server. Adding new and interesting classes is getting increasingly difficult. Would Worgen and Goblins be unique enough just by virtue to encourage players to reroll? Does Blizzard think designing 4 new low-level zones is a good tradeoff to encourage players to reroll? Once a player is at endgame, they are more likely to PvP, PUG, raid, farm, explore, and wait around until the next content patch or expansion hits. If they get bored of the endgame lull, they'll reroll. I doubt Blizzard specifically needs to entice players to reroll, it's something that happens naturally. On the other hand, it's important to add endgame content: a player with lots of max-level toons will eventually get bored of the game and quit if no new endgame content is added after a while.

Therefore, while we might indeed see Worgen and Goblins in the next expansion, I doubt they will be playable races. Just think about Ethereals, Vrykul, Tuskarr, Taunka, and Wolvar, all detailed races and integral parts of the game, but strictly NPC factions.

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