As an arcane mage, I'm planning on playing frost for most fights and arcane in AOE for 7-2. Arcane is looking to be the best AOE spec in 7-2. Arcane is already beating or close to fire on the AOE fights, and with a sizable buff to mark of Aluneth and echoing arcane explosions, it will be even further ahead.
Any speculation could end up being pointless though. They said in the last developer interview that they were going to do a tuning pass after 7-2, before they open ToS.