The official newsletter Blizzard Insider has posted an interview with Lead Designer Tom Chilton about the new PVP system and world PVP options showing up in the Burning Crusade (read the transcript at that link, or listen to audio here).
The interview's pretty softball (hey, what do you expect from an official source), but Chilton does talk a little bit more about the new PVP arena matchups. Players will fight in teams of 2v2, 3v3 or 5v5 from an "arena team" (consisting of main players and benchwarmers) that "has a lot of strong parallels to the guild system" in that you can invite or release players at will. Chilton also answers the question about the arena "seasons"-- matches will be organized in periods of every few months, and at the end of the season, scores will be reset. Chilton says they're planning to change around certain PVP rewards from season to season, and he doesn't rule out the interesting possibility of a "Super Brawl"-- whatever that exactly means.
Chilton also talks a little bit more about 1.12 world PVP in Silithus and Eastern Plaguelands, but here's an interesting question he doesn't answer: Is world PVP only confined to the higher classes? Is Blizzard trying to think of any ways to offer world PVP options to lower levels?
Combined with news from the forums yesterday that players with current PVP titles will be able to keep their highest rank even in the new non-ladder system, it sounds like there are a lot of wacky shakeups coming to PVP in both 1.12 and the expansion. Sounds fun.