Vanilla WoW was balanced :P it gives us flavor if there is something you can't play on both sides besides. But this is ofc subject to change and I am guessing there won't be exclusives to faction but I would if there are like in Vanilla WoW.
Or maybe devs should do something like that:
Necromancer class is not available from the start to the Sacred Order and they will have to do some quests and other requirements to unlock the Necromancer class to put some time/effort (don't make it easy devs :P) in the game to get that class. And same for the other side, Domination players should farm for example for the Paladin class (Just thinking).