They could just make diadem like abyssea from ffxi. Farm for pop items for different NMs for different areas in the zone. All the NMs would drop specific gear. The pops can be farmed from normal mobs around the specific NMs spawn point or their is some kinda trigger pop they work towards, not rng. Even mining or logging could aquire certain pops. Give diadem some actual reason to explore and do stuff in different places. This was the only side of abyssea i enjoyed. The exp zerging prolly killed it for me though.
This would require PF/FC groups only though cause of NM pop goals and coordination. Doesnt sound like diadem is working in DF anyway.
I might even do diadem regardless of trash farming if it had some appealing NM fights on the level of mega bosses. Just my 2 cents.