Yes you can use it as a way to level to 60, Yoshi has said as much. You start as lvl 1 in the dungeon and go up to 60, but only a part of the exp you get will stay in the outside world. So the exp won't be as fast as in the dungeon and they have not compared it to any other way to get exp so I don't know how fast it is compared to regular questing/dungeoning/FATE grind etc, but I would imagine it is at least a decent way to lvl up and from the looks of it I think it will be the most fun to way level up.
