At this point, ladies and gentlemen, it's on like Donkey Kong for the final two weeks. Team rosters are closed, so no team-shuffling is permitted. However, you can create a new team. If you're having roster difficulties or anything of the sort, you'll have to leave or disband your current team and create a new team, which of course will start again in the rating wars.
What are you fighting for? Well, the top 1,000 teams. That's up to 6,000 players, since a 3v3 roster can have up to six people on it, who will all receive a Vanquisher title on the live realms for all characters over level 71. You must have competed in at least 100 3v3 matches on the same character in the same team. Leaving the team is not advisable, since that could reset your score within the rankings and even reset the game's memory of how many matches you've played.
To earn Murkimus, the armored murloc pet, you'll need to play 50 3v3 matches on the same character in the same team. Again, leaving that team may well reset the number of games played, so err on the side of caution.
By having bought into this Arena Pass, once you upgrade your WoW account to Mists of Pandaria, you've secured access to the L90 Arena Pass realm. Blizzard is currently saying that only people who've bought into this Arena Pass will have access to the L90 one, but I suspect that might be subject to change, unless it runs in addition to the usual 2013 Arena Pass.
As Vaneras puts it: