This is not unheard of in the MMORPG world. Everquest 2 with its two player factions (now three, soon four) has patched in the ability for players to betray their racial faction and embrace the other side. This was done due to player demand. Some people want to be able to play with their friends regardless of which race they started with.
The ability to betray to the other player faction was floated to Blizzard pre-TBC and the response was along the lines of "no can do because of the pally/shammie thing." That reasoning is no longer valid. So Blizzard has now retreated to the RP excuse and recommends the petitioner roll a Horde alt.
What do you think? Should you be able to betray if you wanted to? Or should you just level an opposing faction alt to 70 to play with your friends?