For years, the race you played has been indelibly linked with the class and defined how you play the game. Say, for example, you like playing Night Elves, you're limited class-wise to rolling Druid, Priests, Hunters, Rogues and Warriors. On the other hand, if it's a specific class then you are sometimes limited to a particular race. So Draenei are the only Alliance race which can current become Shamans while the same is true, Horde-side, for Blood Elves becoming Paladins.
From a lore perspective, there is little preventing any of these combos. This is especially true as Azeroth expands and the game evolves. But readers, this is new territory for us, as WoW becomes more open. What do you think of the possibility of lore-centric or even playable class and race combinations?