In response to some negative commentary about the arena system Drysc from Blizzard posted the following about season 2.

New items may be added at the start of a new season, depending on progression on the PvE front as well as what PvE content is available. The end/start of a season is only guaranteed to mark the point where the title and armored nether drake rewards are given out. New items being added is dependant upon PvE factors.

To clarify a previous bit of information that we've given out that was incorrect; arena team ratings do not reset at the end of a season. Teams won't have to go through a 'reset period' where they're struggling to regain where they were.

Not all teams are going to have all of the rewards by the second season, in fact the large majority won't. Also, your arena points don't degrade and aren't removed at the end of the season, so you're building points as you go. Even if there are no rewards you want the prospect of new items in the future which you're saving up for, and of course the end of season rewards (title and mount). It wouldn't be very smart to quit playing just because there's nothing to buy, you're still making 'arena money".

You can check out the whole discussion here.