Blizzard is finally giving us a way to host tournaments and leagues without needing to setup our own WoW server. War Games mode allows you to create custom games with a specific map and challenge a specific team. Scheduled to be available along side the release of Cataclysm this is major leap forward in the e-sports scene allowing for anyone to start-up there own tournament or league.
War Games mode
We're simultaneously working on a "war games" mode for battlegrounds that allows groups to challenge other groups to a battle in a specific battleground (including horde vs horde and alliance vs alliance). Granted, the rewards aren't significant, but it's more for players to be able to have fun battling their guildmates and friends or for players on a server to throw down for the sake of pride and bragging rights.
As if that was not enough they are also working on cross-battleground match-ups. This means that you will be able to play against anyone in any battlegroup in your region (e.g. US, Europe, Asia)
Region wide battleground match-ups
We're currently expecting both normal and rated battlegrounds to be cross-battlegroup (within a region) for the launch of Cataclysm. So, players queueing from anywhere in north america could play vs players on any north american battlegroup, etc.
Links
World of Warcraft Forums - War Games mode
World of Warcraft Forums - Cross-Battlegrounds