If I had to throw my hat into the ring, what I would be looking for would be:

- Unique map content/route choices (Eureka Anemos had a great map, not Hydatos or Bozja, which had pretty boring maps)
- Interesting actions (basically everything except Anemos, which had none)
- Bozja queue system for fairness, but requiring people to run to the fates/NMs like Eureka (so there's a cap on combatants, but you can't just AFK in the base all day like bozja)

Those would go a pretty long way into making a new enjoyable field expedition zone for me.