The new arena targeting system allows for macros such as /cast [target=arena1] purge, or /cast [target=arena2] purge. I imagine you get how the 3rd, 4rth, and 5th targets would look now. Also personally I simply have wow macro actions setup in isboxer like /target arena1 and /target arena2 to target the enemy. I also use gladius but I have found the keybinds for gladius are buggy as hell when it comes to targeting.

If you use Isboxer you can also setup a multiple step keybind where your first step is char1 windshear arena1, next step is char2 windshear arena2, and so on.

Oh one last thing, the default blizz arena frames show enemy cast bars now as well ( as does gladius ).