The factional split between the Horde and the Alliance in World of Warcraft has taken a drubbing for a while, simply because the two factions wind up working together to beat one enormous threat or another every single expansion. Frankly, the only place where the strong factional split makes any sense is in the game’s PvP matches. So the developers are responding to this by allowing some cross-factional play… in PvP matches only.
The Mercenary mode is in place when queue times for PvP have gotten out of hand, allowing you to queue and appear as a member of the other faction. The net result will be shorter queues for all and a larger pool of potential players, although you won’t get to see your fantasy of an orc raising his sword alongside draenei.
The next patch will also be rolling out flying in Draenor, which is currently being tested for any bugs or incompatibilities.