Just an idea since Eureka is kinda dead content with no fate spawns.
Rewards EXP until max level in a zone. Then it rewards the zones crystals instead.
In Pagos/Pyros slain leve mobs grant increased kettle crystal gain. A large bonus for the optional hidden hunt mob.
Leve chests could be the same coffers from bunnies.
Could make up for not having Battle Leves in Stormblood. And make Eureka possible to play again.