I would have to pass on arena in this also. I spent 4 years playing WoW and after noticing that 70% of all class nerfs were made for arena balance without even looking at pve balance i could really care less about seeing it in another mmo.
Arenas put a huge microscope on PvP and force a ton of class balance issues that never really work out. One month there is a super combo and they balance it...the next month there is a new synergy combo and the cycle continues.
Arenas add a microscope we don't need.
that is because blizzard managed pvp side of game very poorly, made none of the data i mentioned publically available, and had no rationale behind nerfs / buffs (developers themselves never pvp'ed i bet)
if they follow all of the steps i illustrated on 2nd post to balance the ladder and classes, we can pretty much ignore every negative side-effect arena had on wow's balance
plus if they add 1v1 ladder with the 'matchup weighting system' i mentioned, there is no possible way it can be unbalanced ladder-wise