They would have to really change group dynamics to make 4v4 work and be fun. So many comps I can think of would be unbeatable/unwinnable against. Two scoundrel healer, Guardian tank, sent/slinger comes to mind. With good players, how can it be beat? They could just troll you for 30 minutes until you get pissed and leave the match. That is what a lot of 2v2 games were like during Cata in WoW. A good healer/DPS on both sides and you end up seeing who leaves the arena first... Especially with a mechanic like resolve.
Arena would be a HUGE addition to this game and would attract tons of new/returning players. That, as well as an official 1st season of ranked WZ's(I can only hope) would completely change the 'business as usual', hum-drum days I spend on fleet now.
Fingers crossed.
EDIT: New Ranked gear for Arena that isn't a changed skin of conq...