A few days ago it would have been just mere speculation to suggest that Goblins and Worgen would be playable races in the next expansion. Today however, there’s a bit more to it than just speculation. In the latest PTR Build, four new Halloween Masks were added to the game files of a male and female Goblin and a male and female Worgen. The masks have only ever been of the playable races in the game, so this is definately something to take note of; and the idea of them being playable races isn’t actually too outlandish.
The next expansion will be about the Maelstrom, and convenience has it that that’s where the Goblin City of Undermine is nearby. It’s likely that the Horde will get the Goblins and the Alliance will get the Worgen as that makes the most sense lore-wise. The Horde already have plenty of Goblins sitting about in their cities and running the zeppelins. The Horde also don’t have a “small” race so Goblins will certainly fill that tiny gap. The Worgen could fit in with the Alliance I guess considering they are humans, and maybe they’ve become more civilised since being stuck behind Greymane Wall. It is still speculation, but certainly looks a little more likely.