Players have been suggesting it for a long time and it was always denied, even as recently as a week ago (I think). What made you change your mind on it?

I always felt like Horde side had fewer healers while leveling and Alliance side had fewer tanks (based on my own queue experiences) so I was for the cross-faction dungeon finder. People like to say that both factions have the same kind of players but that's not true. While there's obviously players who play both factions and don't really care, there are many players who exclusively play one side or the other because of the faction theme and aesthetics. Those players are also more likely to play certain roles more than others (like female elves and draenei are more likely to be healers while male orcs or tauren are more likely to be tanks).