I'm a proponent of tiered pop set "NM" content.

Initial items from FATE/Dungeon/Trial/DoL/other...
Use that to pop certain mobs leve-style... receive item...

Require X different items from first stage in order to pop one "NM" from second stage...

etc.

Base item obtainable solo... First stage completable in Light Party... Second stage completable in Full Party...
Final stage requiring 24 member alliance...

The early stages could be done levestyle with final stage being instanced...