Honestly, I didn't expect it'd come so early. Season 4 is now live! Maybe it's a hint that WotLK will also come sooner as expected to not clash with Starcraft 2.
Anyways, with arena season 4 comes the new S4 PvP gear set, which is only accessible from arena vendors and requires arena points.
Right now I have no Information yet on if the S2 gear will now replace the S1 gear which can be bought for regular BG medals and honor points.

If you want to get S4 gear make sure to read into the arena mechanics carefully to avoid frustration. Also train yourself and together with your arena partner in order to be able to compete. The page about Arena PvP on WoWwiki is, as usual, a good place to start.