We've been watching PvP statistics closely, and we couldn't help but notice that there is a huge Alliance bias in the queues - sometimes a hundred Alliance players were in the queue as opposed to only three Horde players - especially in rush hours.
To help this situation somewhat, we implemented Mercenary mode, which in general means that you can choose your faction whenever queueing into random battlegrounds. You can do this by typing .bg faction into your chat, but do keep in mind that the system will always consider your faction upon the moment of joining. Since this feature has originally been implemented in patch 6.2, the current client version is not supporting it, thus further related functions are to be expected later, if any.
This change will become active after a full restart on all realms.
Have a great time!