NOTE: This topic is NOT meant to suggest replacing current mechanics with older ones, but to suggest filling content voids.
...Faction Leves-- Challenging levequests you and your party earn access to, and can then attempt for uncommon, useful gear. Could be an alternate way (from Current Odin/behemoth) of implementing outdoor NMs.
...Hamlet Defense v 2.0-- Guildhest mechanics could easily be used to create a party environment with multiple waves of enemies.
...Chocobo escorts-- Can utilize mechanics from both levequest and guildhest features.
Any other suggestions? The solid ideas on topic I will add to my own.