I really like the concept of Diadem (Though i wish the islands were randomly generated after each maintenance) and got to thinking of ways to improve the experience.

Taking the normal diadem and altering it to work i think would be a good dungeon of sort. I had the following in mind when i was day dreaming about alternative ways to level not involving fates or dungeon grinds.
Unlocked at lv60 like the normal diadem. So you must have at least one job already at 60.
This mode would have no flying or really limited by weather blockades.

Objective list does not go away after you complete four

Objectives reward bonuses per completed objective along the lines of
1st objective +5% experience from mobs
2nd objective +Soul bind, Gathering, Perception ect stat.
3rd objective Law tomes? Wood spoils exchangeable for dungeon equivalent gear?
4th objective Large XP bonus as seen from first completion of a daily dungeon.
5th and so forth stacking similar bonuses as seen fit.