While old fashioned grinding might not be up to snuff, they will have dungeon grinding which is said to give quite a bit of xp. So think of it as like loot with lots of xp on the side!
Edit: kinda hoping that dungeon grinding will be as efficient xp-wise as 1.0's party grinding, but with less fighting over lucrative camps since you'll all be in an instance. Though I think if grinding mobs doesn't turn out to be good enough I can see that getting adjusted in the future.